Re­search quan­ti­fies ge­netic dam­age caused by smok­ing

Kuwait Times - - HEALTH -

WASHINGTON:

Smok­ing a pack of cig­a­rettes a day causes an av­er­age of 150 mu­ta­tions a year in lung cells, ac­cord­ing to a new study that iden­ti­fies spe­cific ways smoke ex­po­sure dam­ages DNA.

The re­search, pub­lished Thurs­day in the jour­nal Science, an­a­lyzes and com­pares tu­mors, pro­vid­ing the first ac­cu­rate mea­sure of the dev­as­tat­ing ge­netic dam­age smok­ing in­flicts not only in lungs but also in other or­gans not di­rectly ex­posed to smoke.

Although it was pre­vi­ously known that smok­ing con­trib­utes to at least 17 types of hu­man can­cers, it had re­mained un­clear ex­actly how cig­a­rettes caused tu­mors, ac­cord­ing to the re­searchers from Bri­tain’s Well­come Trust Sanger In­sti­tute and the Los Alamos Na­tional Lab­o­ra­tory in the United States. Although they saw the largest num­ber of ge­netic mu­ta­tions in lung tis­sue, other parts of the body also dis­played changes in DNA, help­ing ex­plain how smok­ing causes var­i­ous types of can­cer. Cig­a­rettes con­tain more than 7,000 dif­fer­ent chem­i­cals, of which 70 are known to be car­cino­genic, the re­searchers said, point­ing to the com­plex­ity of how smoke in­ter­acts with the body. “This study of­fers fresh in­sights into how to­bacco smoke causes can­cer,” said Lud­mil Alexan­drov of the Los Alamos Na­tional Lab­o­ra­tory, one of the study’s main coau­thors. “Before now, we had a large body of epi­demi­o­log­i­cal ev­i­dence link­ing smok­ing with can­cer, but now we can ac­tu­ally ob­serve and quan­tify the molec­u­lar changes in the DNA due to cig­a­rette smok­ing,” he added. “With this study, we have found that peo­ple who smoke a pack a day de­velop an av­er­age of 150 ex­tra mu­ta­tions in their lungs ev­ery year, which ex­plains why smok­ers have such a higher risk of devel­op­ing lung can­cer.” In the first com­pre­hen­sive anal­y­sis of the DNA of can­cers linked to smok­ing, the sci­en­tists stud­ied more than 5,000 tu­mors, com­par­ing smok­ers’ can­cers with those of peo­ple who had never smoked. They found spe­cific molec­u­lar fea­tures of dam­age in the smok­ers’ DNA, de­ter­mined by the num­ber of those mu­ta­tions in dif­fer­ent tu­mors.

More than 6 mil­lion deaths a year

Although the num­ber of mu­ta­tions within can­cer cells varies be­tween peo­ple, the new study iden­ti­fies the ad­di­tional “mu­ta­tional load” to­bacco smok­ing causes. In other af­fected or­gans, the study shows smok­ing a pack a day causes an es­ti­mated av­er­age of 97 mu­ta­tions in each cell of the lar­ynx; 39 in the phar­ynx; 23 in the mouth; 18 in the blad­der; and six mu­ta­tions in ev­ery cell of the liver each year.

The re­search shows at least five dis­tinct ways smok­ing dam­ages DNA, the most com­mon of which is found in most types of can­cer: ac­cel­er­at­ing the speed of a cel­lu­lar clock that ap­pears to mu­tate DNA pre­ma­turely.

“Our re­search in­di­cates that the way to­bacco smok­ing causes can­cer is more com­plex than we thought,” Mike Strat­ton of Well­come Trust Sanger In­sti­tute said. “In­deed, we do not fully un­der­stand the un­der­ly­ing causes of many types of can­cer,” he added, point­ing to other known causes, such as obe­sity. But the new study of smok­ing-re­lated can­cers can help sci­en­tists bet­ter un­der­stand how all can­cers de­velop and, pos­si­bly, how they can be pre­vented, Strat­ton said. “The genome of ev­ery can­cer pro­vides a kind of ‘ar­chae­o­log­i­cal record,’” in the DNA code, re­flect­ing the ex­po­sure that causes mu­ta­tions, he added. —AFP

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