Changes at global and site-specific DNA methylation of MLH1 gene promoter induced by waterpipe smoking in blood lymphocytes and oral epithelial cells

Abstract

Objective: Cigarette tobacco smoking has been shown to cause cancer through different mechanisms that include epigenetic modulation of tumor-suppressor genes. In the present study, the association between global and MLH1 gene promoter methylation and waterpipe tobacco smoking was investigated.

Materials and Methods: Blood lymphocytes and oral epithelium were sampled from 150 pure waterpipe smokers and 150 never-smokers from Jordan. Methylation assessment was performed using the methylation-specific PCR technique for MLH1 gene and ELISA for global DNA methylation.

Results: Significant increases were shown in global DNA methylation as measured in blood lymphocytes (p < 0.01). In addition, increases in MLH1 gene promoter methylation among waterpipe smokers compared to nonsmokers (p < 0.001) in both oral epithelium and blood lymphocytes was also observed. In addition, strong correlation was found between LWDS-10J dependence score and magnitude of promoter specific methylation of MLH1 (r2 = 0.74–0.78, p < 0.001). Moreover, the percentage of methylated MLH1 promoter was not affected by age or gender (p > 0.05).

Discussion and Conclusion: Collectively, the results indicate that waterpipe tobacco use is associated with epigenetic changes that might predispose users to lung and blood cancers. The results highlight the need for actions to discourage waterpipe smoking and can be used in cessation interventions that target this type of smoking.

Keywords:

• Waterpipe
• tobacco
• epigenetics
• DNA methylation
• global methylation
• MLH1

Acknowledgment

The content is solely the responsibility of the authors and does not necessarily represent the views of the NIH or the FDA.

Disclosure statement

Dr. Eissenberg is a paid consultant in litigation against the tobacco industry and the electronic cigarette industry and is named on a patent for a device that measures the puffing behavior of electronic cigarette users.

Additional information

Funding

This study was supported by the National Cancer Institute (NCI) of the U.S. National Institutes of Health (NIH) under Award Number P30CA016059-34S4. Drs. Eissenberg and Cobb are supported by the National Institute on Drug Abuse of the NIH under Award Number U54DA036105 and the Center for Tobacco Products of the U.S. Food and Drug Administration (FDA).