Carcinogen mmetabolism and DNA adducts in human lung tissues as affected by tobacco smoking or metabolic phenotype: a case-control study on lung cancer patients

Individual variations in activity of pulmonary enzymes that metabolize tobacco-derived carcinogens may affect an individual's cancer risk from cigarette smoking. To investigate whether some of these enzymes (e.g., cytochrome P450IA-related) can serve as markers for carcinogen-induced DNA damage accumulating in the lungs of smokers, non-tumorous lung tissue specimens were taken during surgery from middle-aged men with either lung cancer (n = 54) or non-neoplastic lung disease (n = 20). Phase I (AHH, ECDE) and phase II (EH, UDPGT, GST) enzyme activities, glutathione and malondialdehyde contents were determined in lung parenchyma and/or bronchial tissues; some samples were analyzed for DNA adducts, using ³²P-postlabeling.

Data analysis of subsets or the whole group of patients yielded the following results. (1) Phase I and II drug-metabolizing enzyme (AHH, EH, UDPGT, GST) activities in histologically normal surgical specimens of lung parenchyma were correlated with the respective enzyme activities in bronchial tissues of the same subject. (2) In lung parenchyma, enzyme (AHH, ECDE, EH, UDPGT) activities were significantly and positively related to each other, implying a similar regulatory control of their expression. (3) Mean activities of pulmonary enzymes (AHH, ECDE) were significantly (2- and 7-fold, respectively) higher in lung cancer patients who had smoked within 30 days before surgery (except GST, which was depressed) than in cancer-free subjects with a similar smoking history. (4) In the cancer patients, the time required for AHH, EH and UDPGT activities to return to the level found in non-smoking subjects was several weeks. (5) Bronchial tree and peripheral lung parenchyma preparations exhibited a poor efficiency in activating promutagens to bacterial mutagens in Salmonella. However, they decreased the mutagenicity of several direct-acting mutagens, an effect which was more pronounced in tissue from recent smokers. GSH concentration and GST activity were positively correlated with mutagen inactivation in the same sample. (6) In recent smokers, AHH activity in lung parenchyma was positively correlated with the level of tobacco smoke-derived DNA adducts. (7) Pulmonary AHH and EH activity had prognostic value in tobacco-related lung cancer patients. (8) An enhanced level of pro-oxidant state in the lungs was associated with recent cigarette smoking. Malondialdehyde level in lung parenchyma was associated with the degree of small airway obstruction, suggesting a common free radical-mediated pathway for both lung cancer induction and small airway obstruction.

These results demonstrate the pronounced effect of recent cigarette smoke exposure on pulmonary xenobiotic metabolism and lipid peroxidation and lend further support to the hypothesis that the inducibility of pulmonary AHH activity (cytochrome P450IA1 levels) in tobacco smokers is associated with lung cancer risk. Results on DNA adducts in smokers' lung tissue may help to explain why a certain metabolic phenotype accumulates more DNA damage in lung cells.