 in addition to possessing an extraordinary sweeping activity , pulmonary alveolar macrophages ( pam ) are equipped with the biochemical mechanisms involved in the metabolism of carcinogens , which were found to be inducible in humans by cigarette smoke . moreover , 
 several defense processes were stimulated in rat pam after in vivo administration of the anticarcinogen n - acetylcysteine ( nac ) . 
 benzo[a]pyrene diol epoxide ( bpde)-dna adducts , as revealed by synchronous fluorescence spectrophotometry , were selectively detected in pam of smokers and persisted up to 6 months . 
 the amount of adducts was significantly correlated with the number of currently smoked cigarettes but not with the cigarettes smoked in a lifetime ( pack - years ) . 
 nevertheless , deviations from the regression line pointed out the role of interindividual variability factors in adduct formation . probably due to the low mitotic rate of pam in the respiratory lumen , the frequency of micronuclei 
 was not enhanced in smokers . 
 however , parallel assays in rats showed that micronuclei can be enhanced after massive intratracheal administration of benzo[a]pyrene or whole - body exposure to high amounts of mainstream cigarette smoke , which also induced bpde - dna adducts in lung cells and other organs , including the heart . 
 all these adverse effects were markedly inhibited by the oral administration of nac , which provides the premise and rationale for a future study on the protective effects of oral nac in heavy smokers.imagesfigure 1.figure 1 . 
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