How Secondhand Cigarette Smoke Changes Your Genes

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How Secondhand Cigarette Smoke Changes Your Genes

By Alice Park Friday, Aug. 20, 2010

As if the growing number of smoking bans in restaurants, airplanes and other

public places isn't sending a strong enough message, researchers now have the

first biological data confirming the health hazards of secondhand smoke.

Scientists led by Dr. Crystal at Weill Cornell Medical College documented

changes in genetic activity among nonsmokers triggered by exposure to secondhand

cigarette smoke. Public-health bans on smoking have been fueled by strong

population-based data that links exposure to secondhand cigarette smoke and a

higher incidence of lung diseases such as emphysema and even lung cancer, but do

not establish a biological cause for the correlation. Now, for the first time,

researchers can point to one possible cause: the passive recipient's genes are

actually being affected. (See a new recipe for longevity that says no to

smoking.)

Crystal's team devised a study in which 121 volunteers — some of whom smoked and

some of whom had never smoked — agreed to have samples of their airway cells

studied for genetic activity. The subjects also provided urine so the

researchers could measure the amount of nicotine and its metabolites, like

cotinine, for an objective record of their exposure to cigarette smoke.

Airway cells that line the bronchus, from the trachea all the way to the tiny

alveoli deep in the lungs, are the first cells that confront cigarette smoke,

whether it is inhaled directly from a cigarette or secondhand from the

environment. Crystal's group hypothesized that any deterioration in lung

function associated with cancer or chronic obstructive pulmonary disease,

including emphysema and bronchitis, in which the lungs lose their ability to

take in air, would begin with these cells. (See TIME's guide for good health at

every age.)

And indeed, that's what he and his team found. The researchers removed airway

cells from the volunteers using a bronchoscope and tested all 25,000 identified

human genes in them to determine which ones were active — either turned on or

off — in response to cigarettes. They narrowed the search to 372 genes that were

active among the smokers but not in the cells of the nonsmokers. Based on the

level of nicotine in the urine, the scientists also divided the volunteers into

three groups: smokers, who showed the highest level of the tobacco metabolites;

nonsmokers, who showed none of these compounds and a low-exposure group who fell

in between. Comparing the 372 genes among these three groups, they found that

the low-exposure group shared 34% of the same active genes with nonsmokers and

11% of the same gene activity with smokers. The low-exposure group included both

nonsmokers who have never lit up as well as those who admitted to smoking only

occasionally.

The results suggest that the genetic changes among the low-exposure volunteers,

some of whose exposure is exclusively secondhand, mimicked those of smokers and

represent the first molecular steps toward later lung disease. The study did not

follow the subjects long enough to document what effect the genetic changes may

actually have on the lung tissue, but Crystal says those studies are

forthcoming.

" What is interesting to me is how sensitive the lung cells are to any cigarette

smoke, " he says. " It doesn't matter if you are walking into a cocktail party

where other people are smoking or if you smoke one cigarette a week. No matter

what level of exposure you have, your lung cells know it and they are

responding. It's sort of like canaries in the coal mine — they are crying out

and saying, 'I'm changing here, I'm changing the genes that I turn on and off in

response to this environmental stress.' " (Read about Bavaria's ban on cigarettes

at Oktoberfest.)

It's not clear how permanent these genetic changes are, but previous data

suggests that, at least in smokers, some of the alterations may be irreversible.

Smokers experience a decline in lung function that is accelerated compared with

nonsmokers, and even if they kick the habit, they can never achieve the same

level of function as those who never lit up. If the genetic results are

confirmed, says Crystal, they may help doctors to identify those whose genetic

makeup put them at higher risk of developing lung disease when exposed to

cigarettes, and potentially steer them toward drugs that can help them suppress

the dangerous effects of nicotine on their cells. (Comment on this story.)

In the meantime, the latest findings should reinforce public-health messages

about the dangers of cigarette smoke, even if it is secondhand, says Dr. Norman

Edelman, chief medical officer of the American Lung Association. " When you look

at the biology, there is no safe level of exposure to tobacco smoke, " he says.

" This [study] adds an important piece of evidence that inhaling secondhand smoke

is deleterious and does things to the airway that are not good. "

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