Relation between normal rectal methylation, smoking status, and the presence or absence of colorectal adenomas

Abstract

Background: Colorectal cancer (CRC) is 1 of the leading causes of death in the Western world. CRC develops from premalignant lesions, chiefly colorectal adenomas. Currently, the most accurate and recommended screening method for finding colorectal adenomas is colonoscopy performed on all individuals aged>50 years. However, the costs and risks associated with this procedure are relatively high. The objectives of the current study were to correlate epigenetic alterations that occur in normal rectal mucosa, smoking status, and age with the presence or absence of concomitant colorectal adenomas and to assess the potential clinical value of methylation in normal rectal biopsies as a screening assay for the presence of polyps and, hence, the need for a full colonoscopy.

Methods: One hundred thirteen normal rectal mucosal biopsies from 113 patients were studied. DNA was extracted, modified with sodium bisulfite, and subjected to real-time quantitative, methylation-specific polymerase chain reaction analysis for the following genes: adenomatous polyposis coli (APC); cadherin 1, type 1, E-cadherin (epithelial) (CDH1); estrogen receptor 1 (ESR1); cytokine high in normal 1 (HIN1); hyperplastic polyposis protein 1 (HPP1); O-6 methylguanine-DNA methyltransferase (MGMT); neural epidermal growth factor-like 1 (NELL1); splicing factor 3B, 14-kDa subunit (p14); cyclin-dependent kinase (CDK) inhibitor 2B (inhibits CDK4) (p15); retinoic acid receptor beta (RARβ); somatostatin (SST); tachykinin, precursor 1 (TAC1); and tissue inhibitor of metalloproteinase (TIMP) metallopeptidase inhibitor 3 (TIMP3). Data were then analyzed using several proprietary software programs.

Results: By using several sets of genes, clinical characteristics, and multivariate analyses, the authors developed a prediction model for the presence of concomitant colorectal adenomas at the time of rectal biopsy. They also observed strong correlations between smoking status and rectal methylation pattern and between smoking status and the presence or risk of concomitant adenomas.

Conclusions: A prediction model was developed for the presence of colorectal adenomas based on gene methylation patterns in the normal rectum. The results indicated that these genes may be involved in early stages of adenoma formation. The observed epigenetic alterations in these markers may be caused in part by the effects of smoking and/or age. Normal rectal methylation may be useful as a biomarker for narrowing the population in need of screening colonoscopy.

Figure 1

This receiver operating characteristic curve was based on a linear discriminant analysis model that combined age, and neural epidermal growth factor-like 1 (NELL1), splicing factor 3B 14-kDa subunit (p14), and a methylation index that contained the genes adenomatous polyposis coli (APC), estrogen receptor 1 (ESR1), hyperplastic polyposis protein 1 (HPP1), O-6 methylguanine-DNA methyltransferase (MGMT), p14; cyclin-dependent kinase (CDK) inhibitor 2B (inhibits CDK4) (p15), retinoic acid receptor beta (RARβ), and tachykinin, precursor 1 (TAC1) that distinguished between patients with and without an adenoma at the time of rectal biopsy. Bestpred indicates best prediction.

Figure 2

Average normalized methylation values (NMVs) are illustrated for the genes O-6 methylguanine-DNA methyltransferase (MGMT), retinoic acid receptor beta (RARβ), and somatostatin (SST). This chart demonstrates a trend toward lower methylation in the following sequence: nonsmokers (NS) without adenomas > normal rectal (NR) mucosa from smokers (SM)>NS with adenomas (P) (polyp nonsmoker)>PSM (logarithmic scale). Data were analyzed from 103 NR mucosae and 113 colorectal adenomas.

Figure 3

The risk of developing an adenoma versus age is illustrated in smokers and nonsmokers.