Rocío Rosas-Alonso1, Raúl Galera2, Joan José Sánchez-Pascuala1, Raquel Casitas2, Miranda Burdiel1, Elisabet Martínez-Cerón3, Olga Vera1, Carlos Rodriguez-Antolin1, Olga Pernía1, Javier De Castro1, Francisco García-Rio4, Inmaculada Ibanez-de-Cáceres1. 1. Cancer Epigenetics Laboratory, INGEMM, La Paz University Hospital, Madrid, Spain; Biomarkers and Experimental Therapeutics in Cancer, IdiPAZ, Madrid, Spain. 2. Department of Respiratory Diseases, La Paz University Hospital, IdiPAZ, Madrid, Spain; Spanish Network on Respiratory Diseases (CIBERES), Madrid, Spain. 3. Biomarkers and Experimental Therapeutics in Cancer, IdiPAZ, Madrid, Spain; Spanish Network on Respiratory Diseases (CIBERES), Madrid, Spain. 4. Department of Respiratory Diseases, La Paz University Hospital, IdiPAZ, Madrid, Spain; Spanish Network on Respiratory Diseases (CIBERES), Madrid, Spain; School of Medicine, Autonoma University, Madrid, Spain. Electronic address: fgr01m@gmail.com.
Abstract
INTRODUCTION: MicroRNA-7 (miR-7) has a suppressive role in lung cancer and alterations in its DNA methylation may contribute to tumorigenesis. As COPD patients with emphysema have a higher risk of lung cancer than other COPD phenotypes, we compared the miR-7 methylation status among smoker subjects and patients with various COPD phenotypes to identify its main determinants. METHODS: 30 smoker subjects without airflow limitation and 136 COPD patients without evidence of cancer were recruited in a prospective study. Clinical and functional characteristics were assessed and patients were classified into: frequent exacerbator, emphysema, chronic bronchitis and asthma COPD overlap (ACO). DNA collected from buccal epithelial samples was isolated and bisulfite modified. miR-7 methylation status was evaluated by quantitative methylation-specific polymerase chain reaction (qMSP). RESULTS: miR-7 Methylated levels were higher in COPD patients than in smokers without airflow limitation (23.7±12.4 vs. 18.5±8.8%, p=0.018). Among COPD patients, those with emphysema had higher values of methylated miR-7 (27.1±10.2%) than those with exacerbator (19.4±9.9%, p=0.004), chronic bronchitis (17.3±9.0%, p=0.002) or ACO phenotypes (16.0±7.2%, p=0.010). After adjusting for clinical parameters, differences between emphysematous patients and those with other phenotypes were retained. In COPD patients, advanced age, mild-moderate airflow limitation, reduced diffusing capacity and increased functional residual capacity were identified as independent predictors of methylated miR-7 levels. CONCLUSION: The increase of miR-7 methylation levels experienced by COPD patients occurs mainly at the expense of the emphysema phenotype, which might contribute to explain the higher incidence of lung cancer in these patients.
INTRODUCTION: MicroRNA-7 (miR-7) has a suppressive role in lung cancer and alterations in its DNA methylation may contribute to tumorigenesis. As COPD patients with emphysema have a higher risk of lung cancer than other COPD phenotypes, we compared the miR-7 methylation status among smoker subjects and patients with various COPD phenotypes to identify its main determinants. METHODS: 30 smoker subjects without airflow limitation and 136 COPD patients without evidence of cancer were recruited in a prospective study. Clinical and functional characteristics were assessed and patients were classified into: frequent exacerbator, emphysema, chronic bronchitis and asthma COPD overlap (ACO). DNA collected from buccal epithelial samples was isolated and bisulfite modified. miR-7 methylation status was evaluated by quantitative methylation-specific polymerase chain reaction (qMSP). RESULTS: miR-7 Methylated levels were higher in COPD patients than in smokers without airflow limitation (23.7±12.4 vs. 18.5±8.8%, p=0.018). Among COPD patients, those with emphysema had higher values of methylated miR-7 (27.1±10.2%) than those with exacerbator (19.4±9.9%, p=0.004), chronic bronchitis (17.3±9.0%, p=0.002) or ACO phenotypes (16.0±7.2%, p=0.010). After adjusting for clinical parameters, differences between emphysematous patients and those with other phenotypes were retained. In COPD patients, advanced age, mild-moderate airflow limitation, reduced diffusing capacity and increased functional residual capacity were identified as independent predictors of methylated miR-7 levels. CONCLUSION: The increase of miR-7 methylation levels experienced by COPD patients occurs mainly at the expense of the emphysema phenotype, which might contribute to explain the higher incidence of lung cancer in these patients.