Background: DNA methylation of certain genes is an epigenetic change that is essential for tumorigenesis. Oral submucous fibrosis (OSF) is a precancerous condition of oral mucosa with inflammation and progressive fibrosis of the lamina propria and deeper connective tissue. The hypermethylation of E-cadherin and cyclooxygenase 2 (COX-2) in chronic inflammation may demonstrate a mild lesion/mutation at epigenetic levels. This study compares the hypermethylation status of E-cadherin and COX-2 genes in patients with oral cancer and patients with OSF and also aims to identify risk factors for the development of OSF.
Methods: DNA was extracted from blood samples of 50 healthy subjects, 50 patients with OSF and 60 patients with oral cancer. Methylation-specific polymerase chain reaction for E-cadherin and COX-2 was performed on these samples and the products were analyzed on 2% agarose gel. Surveys about oral health habits and clinical periodontal examinations in patients with OSF and healthy subjects were also conducted by well-trained dentists, and logistic regression was performed to identify risk factors for OSF.
Results: Hypermethylation of E-cadherin and COX-2 was observed in 36% and 22% of oral cancer samples, respectively. In patients with OSF, the rates were 52% and 30%, and in healthy controls the rates were 4% and 6%. Hypermethylation was shown to be correlated between the 3 groups with statistical significance (p<0.01). Methylation of CpG islands in E-cadherin and COX-2 occurred more frequently in patients with OSF than in the control group, but less frequently than in patients with oral cancer. In the logistic regression analysis, smoking, brushing more than twice daily, periodontal probing depth and plaque index were identified as 4 major risk factors for OSF.
Conclusions: These data confirm that E-cadherin and COX-2 expressions are related to OSF. The epigenetic changes presented in patients with chronic inflammation might demonstrate an irreversible destruction in the tissues or organs similar to the effects of cancer. Chronic OSF was significantly associated with hypermethylation, a cancer risk factor.