August 22, 2010

Even Small Tobacco Exposure Poses Serious Genetic Risks

According to a new study, even low levels of tobacco smoke exposure poses a risk to lung health, triggering potentially hazardous genetic changes.

Researcher Ronald Crystal, MD, chief of the division of pulmonary and critical care medicine at New York-Presbyterian/Weill Cornell Medical Center, told WebMD that the hazards of secondhand smoke have been known for years.  "But there were never any studies that had looked at the biology, why this is the case."

His study demonstrates that even the lowest levels of smoke exposure leads to genetic changes at the cellular level in the lungs.  

"What this study shows is, if we could detect nicotine in the urine, we could also detect changes in the number of genes turned on and off'' in the cells of the lungs, Crystal tells WebMD.

Zab Mosenifar, MD, a pulmonologist, director of the Women's Lung Institute, told WebMD that the new findings put "scientific teeth" behind the epidemiology evidence that smoke exposure at low levels is hazardous.

According to the researchers, the study also suggests that those "casual" smokers who think smoking a few cigarettes a week is not hazardous are wrong.

Crystal and colleagues evaluated 121 people, putting them in categories as nonsmokers, low-exposure smokers, or active smokers.

They categorized the people after evaluating their urine for levels of nicotine.

Next, "we took a small sample of the cells lining the airways," Crystal tells WebMD. "The cells lining the inside of your airways are called epithelial cells.'' He says that when you puff a cigarette, these are the first cells affected.

The researchers scanned each person's entire genome to figure out which genes were activated or deactivated in the cells lining the airways.

"When exposed to smoke, the genes get turned on and off abnormally," he says. "The cell is crying out at a biological level, saying, 'Something's wrong. I'm being stressed here.'"

He says that about 370 different genes sense the smoke, and turn off and on in the area.

Crystal told WebMD that eventually the genetic discoveries may help experts determine why some people are more susceptible to the health effects of smoke exposure than others are.

''What they have shown is that these epithelial cells inside the small airways contain very sensitive genes," Mosenifar told WebMD.

"These cells, they have these antennae, they pick up very low levels of tobacco. Small airway epithelium is very sensitive," he says.  "This says basically even a small amount of exposure to smoke does create changes at the cellular level in genetically susceptible people."

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