Are benzo[a]pyrene-DNA adducts an accurate biomarker of long-term in utero exposure to smoking?

BACKGROUND: Maternal smoking during pregnancy is associated with adverse perinatal outcomes. In view of concerns about underreporting, benzo[a]pyrene (B[a]P)-DNA adducts could be used to provide information about long-term in utero exposure to smoking but have not previously been used with samples from neonates. This study aimed to verify whether B[a]P-DNA adducts could accurately assess tobacco smoke exposure during fetal life. The objectives were to correlate B[a]P-DNA adduct levels with active maternal and passive smoking and to determine the sensitivity and specificity of smoking and nonsmoking status by comparing neonatal B[a]P-DNA adduct levels with those of maternal self-reports. MATERIALS AND METHODS: B[a]P-DNA adducts in neonatal buccal cell samples were determined by a competitive immunoassay. Three groups of neonates were constituted according to maternal self-reported smoking status during pregnancy: nonsmokers (n=25; control group), <10 cigarettes per day (n=18; S- group), or >10 cigarettes per day (n=21; S+ group). RESULTS: The mean B[a]P-DNA adduct level rose significantly when comparing the controls with the S- and S+ groups. Maternal active smoking had the strongest effect on B[a]P-DNA adduct levels in neonates. A cross analysis between B[a]P-DNA adduct levels and maternal self-reported levels revealed high sensitivity and specificity. CONCLUSIONS: This preliminary study suggests that B[a]P-DNA adducts are reliable biomarkers for the screening of long-term in utero exposure to smoking and are accurate when compared with maternal self-reported levels of active smoking. Detection of B[a]P-DNA adducts in neonates could provide a useful, noninvasive tool in clinical risk assessment studies but would benefit from further confirmation with another validated biomarker.

Effects of type of smoking (pipe, cigars or cigarettes) on biological indices of tobacco exposure and toxicity.

Although all forms of smoking are harmful, smoking pipes or cigars is associated with lower exposure to the lethal products of tobacco products and lower levels of morbidity and mortality than smoking cigarettes. Cytochrome P-450-1A (CYP1A) is a major pathway activating carcinogens from tobacco smoke. Our primary aim was to compare CYP1A2 activity in individuals smoking pipes or cigars only, cigarettes only and in non-smokers. We studied 30 smokers of pipes or cigars only, 28 smokers of cigarettes only, and 30 non-smokers male subjects matched for age. CYP1A2 activity was assessed as the caffeine metabolic ratio in plasma. One-day urine collection was used for determining exposure to products of tobacco metabolism. Nitrosamine and benzo[a]pyrene DNA adducts were measured in lymphocytes. CYP1A2 activity was greater (p<0.0001) in cigarette smokers (median: 0.61; interquartile range: 0.52-0.76) than in pipe or cigar smokers (0.27; 0.21-0.37) and non-smokers (0.34; 0.25-0.42) who did not differ significantly. Urinary cotinine and 1-hydroxypyrene levels were higher in cigarette smokers than in pipe or cigar smokers and higher in the later than in non-smokers. DNA adducts levels were significantly lower in pipe or cigar smokers than in cigarette smokers. In multivariate analysis, cigarette smoking was the only independent predictor of CYP1A2 activity (p<0.0001) and of 1-hydroxypyrene excretion in urine (p=0.0012). In this study, pipe or cigar smoking was associated with lower exposure to products of tobacco metabolism than cigarette smoking and to an absence of CYP1A2 induction. Cigarette smoking was the only independent predictor of CYP1A2 activity in smokers. However, inhalation behaviour, rather than the type of tobacco smoked, may be the key factor linked to the extent of tobacco exposure and CYP1A2 induction. Our results provide a reasonable explanation for the results of epidemiological studies showing pipe or cigar smoking to present fewer health hazards than cigarette smoking.

A competitive ELISA detecting 7-methylguanosine adduct induced by N-nitrosodimethylamine exposure.

N-Nitrosodimethylamine is a chemical compound known to be carcinogenic to animals and probably to humans. It is widespread and it can be found in food, tobacco smoke and in industrial emissions, such as in the rubber industry. N-Nitrosodimethylamine exerts its biological effects after metabolic activation by forming methylating nucleic acids in DNA. The most formed adduct is 7-methylguanosine. Our laboratory has developed and validated a competitive enzyme-linked immunosorbent assay in order to detect this adduct in DNA exposed to N-nitrosodimethylamine in vitro or in vivo. The imidazole ring-opening (iro) of 7-methylguanosine was required because of its stability. When 7-methylguanosine iro and serum were incubated at 4 degrees C, the assay was 35 times more sensitive than at 37 degrees C (50% inhibition at 37 fmol 7-methylguanosine iro per well at 4 degrees C and 1.28 pmol at 37 degrees C) with a lower limit of detection at 1.58 fmol 7-methylguanosine iro. This assay is reproducible, can be routinely performed and is sensitive enough to detect 7-methylguanosine adduct in DNA samples from human exposed to N-nitrosodimethylamine. We aim to use this method in further studies on epidemiological assessment in people at high risk, such as smokers.