In yet another study on the harmful biologic effects of tobacco, there is a new concern for smokers and non-smokers alike. Cigarette smoking can alter thousands of genes through the process of DNA methylation. The new study was published in the journal Cardiovascular Genetics. Researchers reviewed blood samples of almost 16000 people and found that methylation from tobacco smoke predisposes people to cancer, osteoporosis, lung disease, cardiovascular disease and other inflammatory diseases. Although the study was emphasizing the long term side effects of smoking, there is some good news for non-smokers. The sooner you quit smoking the better, as it was found that further gene damage can be stopped, and even reversed.
Tobacco Smoke Exposure Adds Methyl to DNA
Tobacco products have compounds called methyl, a by-product of methane. The process of DNA methylation adds methyl into the genes of smokers and is known to represses gene transcription. Methylation leaves a long-term stamp on a smoker’s DNA and is a mechanism that makes tobacco exposure responsible for many smoking-related diseases. The level of methylation in a smoker is dependent on two factors:
• daily tobacco smoke exposure
• years of smoke exposure
The aim of the research was to determine comprehensively any association between tobacco and DNA methylation. Co-author and deputy chief of epidemiology Doctor Stephanie London, lead the team of researchers from the National Institute of Environmental Health Sciences. They conducted a detailed analysis of DNA methylation for the entire human genome, using 16000 participants who gave their DNA from blood samples. They were divided into these groups:
• 2,433 current smokers
• 6,518 former smokers
• 6,956 non-smokers
Comparison studies were done on the following groups:
• current versus non-smokers
• former versus non-smokers
Not surprising, current smokers showed a significant DNA methylation of over 1,405 genes. These genes were already associated as being vulnerable to DNA damage due to cigarette smoke, according to several genome studies already published. It is this DNA damage which leads to smoking-related diseases. In former smokers, the study found a pattern of altered methylation, meaning DNA damage will slow down. While this may seem like good news for former smokers, it indicates that genome methylation will persist for many years after discontinuing cigarettes.
Smoking Related Deaths are Mostly Preventable
Doctor Norman Edelman, who is a senior scientific advisor for the American Lung Association, says the best message from this report is that cigarette smoking has a pervasive impact on your genes. For smokers and non-smokers, much of the genetic damage can be reversible, but not totally. Doctor London says smoking contributes to many diseases, which cause more than 6 million deaths worldwide every year and are mostly preventable.
The report concludes that cigarette smoke has a broad impact on genome-wide DNA, due to the damage from methylation. Although further damage can be avoided by quitting smoking, some genetic changes can persist for many decades afterwards. The good news is that researchers have discovered a few novel methylated genes that could serve as stable biomarkers. This could be used to measure the biological effects of smoking and might lead to therapies for the prevention and treatment of diseases caused by tobacco smoke.