Effects of obesity, and of weight loss following bariatric surgery, on methylation of DNA from the rectal mucosa and in cell-free DNA from blood.

BACKGROUND: DNA methylation is an epigenetic mechanism through which environmental factors including nutrition and inflammation influence health. Obesity is a major modifiable risk factor for many common diseases including cardiovascular diseases and cancer. In particular, obesity-induced inflammation resulting from aberrantly-methylated inflammatory genes may drive risk of several non-communicable diseases including colorectal cancer (CRC). This study is the first to investigate the effects of weight loss induced by bariatric surgery (BS) on DNA methylation in the rectum and in cell-free DNA (cfDNA) from blood. SUBJECTS AND METHODS: DNA methylation was quantified in rectal mucosal biopsies and cfDNA from serum of 28 participants with obesity before and 6 months after BS, as well as in 12 participants without obesity (control group) matched for age and sex from the Biomarkers Of Colorectal cancer After Bariatric Surgery (BOCABS) Study. DNA methylation of LEP, IL6, POMC, LINE1, MAPK7 and COX2 was quantified by pyrosequencing. RESULTS: BMI decreased significantly from 41.8 kg/m2 pre-surgery to 32.3 kg/m2 at 6 months after BS. Compared with the control group, obesity was associated with lower LEP methylation in both the rectal mucosa and in cfDNA from serum. BS normalised LEP methylation in DNA from the rectal mucosa but not in cfDNA. BS decreased methylation of some CpG sites of LINE1 in the rectal mucosal DNA and in cfDNA to levels comparable with those in participants without obesity. Methylation of POMC in rectal mucosal DNA was normalised at 6 months after BS. CONCLUSION: BS reversed LINE1, POMC and LEP methylation in the rectal mucosa of patients with obesity to levels similar to those in individuals without obesity. These findings support current evidence of effects of BS-induced weight loss on reversibility of DNA methylation in other tissues. The DNA methylation changes in the rectal mucosa shows promise as a biomarker for objective assessment of effects of weight loss interventions on risk of cancer and other diseases.