Carcinogens In Tobacco Smoke Research Articles

P53 Mutations in Benzo(a)Pyrene-Exposed Human p53 Knock-in Murine Fibroblasts Correlate with p53 Mutations in Human Lung Tumors

Human p53 mutation spectra differ significantly from one cancer type to another. One possible reason is that carcinogenic risk factors differ, and these factors elicit distinct mutation patterns. There has been no mammalian assay, however, with which to generate mutation patterns in human p53 sequences experimentally, hampering interpretation of the human tumor spectra. We have designed a new mammalian cell assay using gene targeting technology that selects and scores human p53 gene sequence mutations in human-p53 knock-in (Hupki) murine embryonic fibroblasts (HUF) that have undergone immortalization. With the Hupki assay we examined here whether benzo(a)pyrene (BaP), a major tobacco smoke carcinogen could elicit p53 mutation patterns characterizing the human lung tumor p53 mutation spectrum. We found that, in contrast to unexposed HUFs or HUFs exposed to other carcinogenic agents, HUFs exposed to BaP acquire mutations that display major features of the human lung tumor p53 mutation spectrum: (a) predominance of G-to-T mutations, (b) unequivocal strand bias of the transversions, and (c) a mutation hotspot at codons 157 to 158. These data are consistent with the hypothesis that BaP has a direct role in causing smokers' lung tumor p53 mutations. The assay can be used to examine various hypotheses on the endogenous or exogenous factors responsible for the p53 mutations in human tumors arising in other tissues.

HPRT gene alterations in umbilical cord blood T-lymphocytes in newborns of mothers exposed to tobacco smoke during pregnancy

Prenatal exposure to tobacco smoke has been associated with an increased risk of pediatric malignancies, yet the transplacental induction of genetic alterations by tobacco smoke carcinogens and their implication to childhood diseases remain poorly understood. We characterized mutations in the HPRT gene in umbilical cord blood T-lymphocytes of self-reported 103 never-smoking mothers and 104 smoking mothers (54 mothers smoked throughout and 50 mothers quit smoking during pregnancy). The results showed the illegitimate V(D)J recombinase-mediated deletion of HPRT exons 2–3 was the most prominent alteration occurring in 48.2% (26/54) of mutants from neonates of the smoking mothers who smoked during pregnancy, compared with 28.0% (14/50) from those of smoking mothers who quit smoking during pregnancy ( p = 0.035, Fisher's exact test), 34.9% (36/103) from never-smoking mothers ( p = 0.08), or 32.7% (50/153) of those of neonates born from the latter two groups of mothers combined ( p = 0.043). There was no significant difference in the frequency of this deletion between neonates of the never-smoking mothers and the smoking mothers who quit smoking during pregnancy (34.9% versus 28.0%, respectively, p = 0.39). The results show an increase in illegitimate V(D)J recombinase-mediated deletion of HPRT exons 2–3 in cord blood T-lymphocytes of newborns of mothers who smoked during pregnancy, compared with the group of mothers who did not smoke during pregnancy, implying an increase in illegitimate V(D)J recombinase-mediated alteration, a genetic recombination event associated with childhood malignancies, may be induced in utero during pregnancy by maternal exposure to tobacco smoke-derived genotoxicants.

Racial differences in exposure and glucuronidation of the tobacco‐specific carcinogen 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK)

In the United States, Blacks who smoke cigarettes have a higher mean blood concentration of the nicotine metabolite cotinine than White smokers. It has not been determined whether there are racial differences in the exposure to the cigarette smoke carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and in the detoxification of NNK metabolites. A community-based cross-sectional survey of 69 Black and 93 White smokers was conducted in lower Westchester County, New York. Information on smoking and lifestyle habits was collected and urinary concentrations of several tobacco smoke biomarkers were compared, including the NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide (NNAL-Gluc). A frequency histogram and probit plot of NNAL-Gluc:NNAL ratios were constructed to determine slow and rapid glucuronidation phenotypes. The mean concentrations of total NNAL, urinary cotinine, plasma cotinine, and thiocyanate were significantly higher in Black men than in White men for each cigarette smoked. In women, the only biomarker that was significantly elevated in Blacks was plasma cotinine. A higher proportion of White versus Black women was categorized as "rapid" glucuronidators (two-tailed exact test, P = 0.03). In men, there were no significant differences in NNAL-Gluc:NNAL phenotypes. The higher rates of lung carcinoma in black men may be due in part to a higher level of exposure to tobacco smoke carcinogens.

β-Carotene interaction with NNK in the AJ-mouse model: Effects on cell proliferation, tumor formation and retinoic acid responsive genes

We studied the influence of beta-carotene on the tobacco smoke carcinogen 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor development in the A/J-mouse model. The normally low beta-carotene absorption was facilitated with a diet enriched in fat and bile salt, resulting in plasma and lung tissue levels similar to humans. beta-Carotene enhanced NNK-induced early bronchial cell proliferation, however, this effect was not predictive for later tumor development. Tumor multiplicity was not significantly affected by beta-carotene, neither in carcinogen-initiated nor in uninitiated mice, and regardless of dose and time point of supplementation during tumor development. RARbeta isoform and CYP26 gene expression levels analyzed by quantitative RT-PCR were weakly, but significantly, inversely correlated and showed evidence for altered retinoid signaling and catabolism in the lungs of NNK-initiated, beta-carotene supplemented mice. However, this interaction did not translate into enhanced tumor multiplicity. These results indicate that impaired retinoid signaling is not likely a key factor in lung tumorigenesis in this mouse model.

Benzo[a]pyrene diol epoxide-induced 9p21 aberrations associated with genetic predisposition to bladder cancer.

CDKN2A, 9p21, encodes two alternatively spiked, functionally distinct, tumor-suppressor proteins, P16INK4A and P14ARF, which play active roles in the RB1 and TP53 pathways, respectively. Deletion of 9p is one of the most frequent genomic alterations in bladder cancer. In addition, alterations of 9p21 and P16 are frequently seen in the epithelial cells of chronic smokers. This pilot study evaluated whether 9p21 aberrations induced by exposure in vitro to benzo[a]pyrene diol epoxide (BPDE), the metabolic product of benzo[a]pyrene, a constituent of tobacco smoke, were more common in the peripheral blood lymphocytes of 61 bladder cancer patients compared to 64 matched controls. Our hypothesis was that 9p21 sensitivity to BPDE reflects the susceptibility of a specific locus to damage from carcinogens in tobacco smoke. We found that BPDE-induced chromosome band 9p21 aberrations were significantly higher in lymphocytes of bladder cancer cases (24.97 +/- 5.26 per 1,000) than in controls (20.72 +/- 4.51 per 1,000; P < 0.0001). However, no difference was observed for CEP9, a control locus. After adjustment for age, sex, ethnicity, and smoking status, 9p BPDE sensitivity had an odds ratio (OR) of 9.01 [95% confidence interval (95% CI) 3.75, 21.67] for bladder cancer. We further observed a gradient of elevated bladder cancer risk associated with increasing chromosomal damage. The adjusted ORs for subjects in the second, third, and highest quartiles of BPDE-induced 9p21 aberrations relative to the first quartile were 0.48 (0.04, 5.69), 5.14 (1.12, 23.59), and 21.51 (4.75, 97.34), respectively, providing increasing dose-response evidence of the locus-specific alterations. Thus, 9p21 may be a molecular target for BPDE-induced damage in bladder cancer cases.

Benzo[ a]pyrene-enhanced mutagenesis by asbestos in the lung of λ-lacI transgenic rats

To study the suspected mechanism of the interaction between tobacco smoking and asbestos exposure in the modulation of cancer risk, the mutagenic potential of asbestos in combination with the tobacco smoke carcinogen benzo[ a]pyrene (B[ a]P) was examined in vivo in the rat lung. B[ a]P was administered intratracheally in one set of experiments, or by two daily intraperitoneal injections in another set of experiments, to λlacI transgenic rats, together with 1, 2 or 4 × 2 mg amosite in one experiment. In the first experiment, the combined action of amosite and B[ a]P caused a synergistic (superadditive) increase of mutation frequency in the lung, as compared to groups treated only with asbestos or B[ a]P. In the second experiment, i.p. treatment with B[ a]P did not significantly alter the mutation frequency induced by amosite, neither after 4 nor after 16 weeks of exposure. The B[ a]P-DNA adduct levels were unaffected by amosite co-treatment in both experiments. We assume that the synergistic increase of mutation frequency after intratracheal treatment was due to the mitogenic activities of B[ a]P and of amosite. In conclusion, our findings indicate that a weak and delayed mutagenic effect of amosite in rat lung observed in another study was strongly enhanced by the concomitant action of B[ a]P. The striking enhancement effect of B[ a]P may provide a basis for understanding the suspected synergism of smoking on asbestos carcinogenesis.

Increased Susceptibility of Mice Lacking Clara Cell 10-kDa Protein to Lung Tumorigenesis by 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone, a Potent Carcinogen in Cigarette Smoke

Ninety percent of all human lung cancers are related to cigarette smoking. Both tobacco smoke and lung tumorigenesis are associated with drastically reduced levels of Clara cell 10-kDa protein (CC10), a multifunctional secreted protein, naturally produced by the airway epithelia of virtually all mammals. We previously reported that the expression of CC10 is markedly reduced in animals exposed to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK, a potent carcinogen in tobacco smoke. Furthermore, it has been reported that CC10 expression, induced in certain tumor cells, reverses the transformed phenotype. We demonstrate here that NNK exposure of CC10-knock-out (CC10-KO) mice causes a significantly higher incidence of airway epithelial hyperplasia and lung adenomas compared with wild type (WT) littermates (30% CC10-KO versus 5% WT, p = 0.041). We also found that compared with NNK-treated WT mice, CC10-KO mice manifest increased frequency of K-ras mutation, elevated level of Fas ligand (FasL) expression, and increased MAPK/Erk phosphorylation, all of which are considered predisposing events in NNK-induced lung tumorigenesis. We propose that CC10 has a protective role against NNK-induced lung tumorigenesis mediated via down-regulation of the above-mentioned predisposing events.

No Association between the XPD 312, 751, or XRCC1 399 Polymorphisms and K-ras Gene Mutation in Smoking Non-Small-Cell Lung Cancer

No Association between the <i>XPD</i> 312, 751, or <i>XRCC1</i> 399 Polymorphisms and K-ras Gene Mutation in Smoking Non-Small-Cell Lung Cancer

Genetic polymorphism of the human cytochrome CYP2A13 in a French population: implication in lung cancer susceptibility

The human cytochrome CYP2A13, which is mainly expressed in the respiratory tract, has been shown to be highly efficient in vitro in the metabolism of tobacco-smoke carcinogens and procarcinogens such as 4-methylnitroso-1-(3-pyridyl)-1-butanone (NNK). In order to investigate the extent of CYP2A13 genetic polymorphism in a French Caucasian population of 102 individuals, a screening for sequence variations in the 5 ′-untranslated and protein encoding regions of its gene was performed using a polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) strategy. Six polymorphisms in the coding region were identified, including two rare missense mutations (C474G or Asp 158Glu, G967T or Val 323Leu) and one nonsense mutation (Arg 101Stop). This deleterious mutation, the most frequent (5%) in our population, presumably encodes a severely truncated protein. The influence of the nonsense mutation in lung cancer susceptibility was examined by PCR-SSCP using peripheral blood DNA from 204 cases of lung cancer and 201 controls. The CYP2A13*7 allele, which harbours the C301T mutation, was present in 2.0% of controls and 3.4% of cases. However, multivariate analysis showed an elevated risk for small cell lung cancer in subjects heterozygous for the null allele (odds ratio OR=9.9; 95% confidence interval CI=1.9–52.2). This increased risk was not linked to other histological types of lung cancer.

Carcinogen derived biomarkers: applications in studies of human exposure to secondhand tobacco smoke

Objective: To review the literature on carcinogen derived biomarkers of exposure to secondhand tobacco smoke (SHS). These biomarkers are specifically related to known carcinogens in tobacco smoke and include urinary...

Genetic polymorphisms of MPO, COMT, MnSOD, NQO1, interactions with environmental exposures and bladder cancer risk

Tobacco smoking and occupational exposure are major risk factors of bladder cancer via exposure to polycyclic aromatic hydrocarbons (PAHs) and aromatic amines, which lead to oxidative stress and DNA damage. Several enzymes, which play key roles in oxidative stress are polymorphic in humans. Myeloperoxidase (MPO) produces a strong oxidant for microbicidal activity, and activates carcinogens in tobacco smoke. Catechol-O-methyltransferase (COMT) catalyzes the methylation of endo- and xenobiotics and prevents redox cycling. NAD(P)H:quinone oxidoreductase (NQO1) catalyzes the two-electron reduction of quinoid compounds, which also protects cells from redox cycling. Manganese superoxide dismutase (MnSOD) protects cells from free radical injury. To test the hypothesis that the risk of bladder cancer can be influenced by polymorphisms in the genes that modulate oxidative stress, in particular by interacting with environmental carcinogens, we conducted a hospital-based case-control study among men in Brescia, Northern Italy. We recruited and interviewed 201 incident cases and 214 controls from 1997 to 2000. Occupational exposures to PAHs and aromatic amines were coded blindly by occupational physicians. Unconditional multivariate logistic regression was applied to model the association between genetic polymorphisms and bladder cancer risk and the effect of modifications of smoking and occupational exposures were evaluated. MPO G-463A homozygous variant was associated with a reduced risk of bladder cancer with an OR of 0.31 (95% CI = 0.12-0.80). MnSOD Val/Val genotype increased the risk of bladder cancer with OR of 1.91 (95% CI = 1.20-3.04), and there was a combined effect with smoking (OR = 7.20, 95% CI = 3.23-16.1) and PAH (OR = 3.02, 95% CI = 1.35-6.74). We did not observe an effect of COMT Val108Met polymorphism. These findings suggest that individual susceptibility of bladder cancer may be modulated by MPO and MnSOD polymorphisms, and that the combination of genetic factors involved in oxidative stress response with environmental carcinogens may play an important role in bladder carcinogenesis.

Menthol pharmacology and its potential impact on cigarette smoking behavior.

Menthol is the only tobacco additive promoted and advertised by the tobacco industry. Although a considerable body of research has examined the effects of menthol when it is administered alone and unburned, the effects of menthol when burned in cigarette smoke are more complex because it is administered in a matrix of more than 4,000 substances. Therefore, it is difficult to isolate potential pharmacological and toxic effects of menthol when it is administered in a smoke mixture. Menthol properties include cooling and local anesthesia, as well as effects on drug absorption and metabolism, bronchodilation and respiration changes, and electrophysiology. Subjective effects of smoothness and less harshness have been identified as reasons for menthol cigarette smoking, but findings have been inconclusive regarding the effect of menthol on carbon monoxide exposure and smoking topography parameters. Gaps in the research literature and future research areas include the following: (a) What is the role of menthol in tobacco reinforcement and addiction? (b) In the absence of nicotine, is menthol reinforcing? (c) Are the pharmacological and physiological effects of menthol mediated by a menthol-specific receptor or some other central nervous system-mediated action? (d) What are the influences of menthol and menthol metabolism on the metabolic activation and detoxification of carcinogens in tobacco smoke? and (e) Do differences exist in cigarette smoking topography in relation to the interaction of ethnicity, gender, and menthol cigarette preference? Answers to these questions will help to elucidate the function of menthol in cigarettes and its impact on smoking behavior.

Detection of UGT1A10 polymorphisms and their association with orolaryngeal carcinoma risk.

UGT1A10 exhibits glucuronidating activity against metabolites of the tobacco smoke carcinogen, benzo(a)pyrene, and is expressed highly in numerous target tissues for tobacco-related cancers including the upper aerodigestive tract. The current study was conducted to determine the prevalence of genetic polymorphisms in the UGT1A10-specific region of the UDP-glucuronosyltransferase family 1A locus and their relationship with risk for orolaryngeal carcinoma. The authors analyzed UGT1A10-specific sequences in a population of black, white, and Asian individuals. Ten UGT1A10 alleles were identified by direct sequencing of UGT1A10 sequences amplified by polymerase chain reaction (PCR) using DNA purified from buccal cell swabs that were taken from individual subjects. In addition to three silent polymorphisms, three missense polymorphisms were found at codons 139 (Glu > Lys), 240 (Thr > Met), and 244 (Leu > Ile). Using PCR-restriction fragment length polymorphism analysis of buccal cell DNA, the prevalence of the UGT1A10(240Met) variant was less than 0.01% in whites and blacks. Similarly, the prevalence of both the UGT1A10(139Lys) and UGT1A10(244Ile) variants was less than 0.01% in whites but it was significantly higher (0.04 and 0.05, respectively, P < 0.01) in blacks. None of the missense UGT1A10 variants were found in any of the Asian individuals examined. In a case-control study of black individuals, a significant association with orolaryngeal carcinoma risk was found in persons with at least 1 UGT1A10(139Lys) allele (crude odds ratio, 0.29 [95% confidence interval, 0.10-0.81]; adjusted odds ratio, 0.20 [95% confidence interval, 0.05-0.87]). No association was observed for the codon 244 (Leu > Ile) polymorphism. The data from the current study show that the UGT1A10 gene has several low-frequency missense polymorphisms and that the codon 139 polymorphism is an independent risk factor for orolaryngeal carcinoma in blacks.

An analysis of the role of tobacco-specific nitrosamines in the carcinogenicity of tobacco smoke.

Cigarette smoke is a complex mixture consisting of more than 4500 chemicals, including several tobacco-specific nitrosamines (TSNA). TSNA typically form in tobacco during the post-harvest period, with some fraction being transferred into mainstream smoke when a cigarette is burned during use. The most studied of the TSNA is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNK has been shown to be carcinogenic in laboratory animals. Studies examining the carcinogenicity of NNK frequently are conducted by injecting rodents with a single dose of 2.5 to 10 mumol of pure NNK; the amount of NNK contained in all of the mainstream smoke from about 3700 to 14,800 typical U.S. cigarettes. Extrapolated to a 70-kg smoker, the carcinogenic dose of pure NNK administered to rodents would be equivalent to the amount of NNK in all of the mainstream smoke of 22 to 87 million typical U.S. cigarettes. Furthermore, extrapolating results from rodent studies based on a single injection of pure NNK to establish a causative role for NNK in the carcinogenicity of chronic tobacco smoke exposure in humans is not consistent with basic pharmacological and toxicological principles. For example, such an approach fails to consider the effect of other smoke constituents upon the toxicity of NNK. In vitro studies demonstrate that nicotine, cotinine, and aqueous cigarette "tar" extract (ACTE) all inhibit the mutagenic activity of NNK. In vivo studies reveal that the formation of pulmonary DNA adducts in mice injected with NNK is inhibited by the administration of cotinine and mainstream cigarette smoke. Cigarette smoke has been shown to modulate the metabolism of NNK, providing a mechanism for the inhibitory effects of cigarette smoke and cigarette smoke constituents on NNK-induced tumorigenesis. NNK-related pulmonary DNA adducts have not been detected in rodents exposed to cigarette smoke, nor has the toxicity of tobacco smoke or tobacco smoke condensate containing marked reductions in TSNA concentrations been shown to be reduced in any biological assay. In summary, there is no experimental evidence to suggest that reduction of TSNA will reduce the mutagenic, cytotoxic, or carcinogenic potential of tobacco smoke.

Association of Cigarette Smoking with Extraprostatic Prostate Cancer in Young Men

Association of Cigarette Smoking with Extraprostatic Prostate Cancer in Young Men

The Development of Chronic Obstructive Pulmonary Diseases Correlates with Microsatellite DNA Instability

Allele distribution at a highly polymorphic minisatellite adjacent to the c-Hras1 gene as well as deletions of microsatellite markers, D3S966, D3S1298, D9S171, and a microsatellite within p53 gene, were examined in bronchial epithelium specimens obtained from 53 chronic obstructive pulmonary disease (COPD) patients and healthy donors. A higher frequency of rare Hras1minisatellite alleles in COPD patients than in the individuals without pulmonary pathology (6.6% versus 2.2%; P < 0.05) was shown. This difference was most pronounced in the group of ten COPD patients with idiopathic pulmonary fibrosis. Three of these patients had rare Hras1 minisatellite allele (P < 0.02 in comparison with healthy controls). Alterations in at least one of the microsatellite markers (deletions or microsatellite instability) were detected in bronchial epithelium samples obtained from: 4 of 10 COPD patients with pneumofibrosis (40%); 15 of 43 COPD patients (34.9%) without pneumofibrosis; and 8 of 20 tobacco smokers (40%) without pulmonary pathology. These defects were not observed in the analogous samples obtained from healthy nonsmoking individuals. No statistically significant differences were revealed between COPD patients and healthy smokers upon comparison of both the total number of molecular defects and the number of defects in the individual chromosomal loci. The total number of molecular defects revealed in bronchial epithelium samples from the individuals of two groups examined correlated with the intensity of exposure to tobacco smoke carcinogens (r = 0.28; P < 0.05). These findings suggest that rare alleles at theHras1 locus may be associated with hereditary predisposition to COPD and the development of pneumofibrosis, while mutations in microsatellite markers result from exposure to tobacco smoke carcinogens and are not associated with the appearance of these pathologies.

Tobacco smoke carcinogens, DNA damage and p53 mutations in smoking-associated cancers.

It is estimated that cigarette smoking kills over 1 000 000 people each year by causing lung cancer as well as many other neoplasmas. p53 mutations are frequent in tobacco-related cancers and the mutation load is often higher in cancers from smokers than from nonsmokers. In lung cancers, the p53 mutational patterns are different between smokers and nonsmokers with an excess of G to T transversions in smoking-associated cancers. The prevalence of G to T transversions is 30% in smokers' lung cancer but only 12% in lung cancers of nonsmokers. A similar trend exists, albeit less marked, in laryngeal cancers and in head and neck cancers. This type of mutation is infrequent in most other tumors aside from hepatocellular carcinoma. At several p53 mutational hotspots common to all cancers, such as codons 248 and 273, a large fraction of the mutations are G to T events in lung cancers but are almost exclusively G to A transitions in non-tobacco-related cancers. Two important classes of tobacco smoke carcinogens are the polycyclic aromatic hydrocarbons (PAH) and the nicotine-derived nitrosamines. Recent studies have indicated that there is a strong coincidence of G to T transversion hotspots in lung cancers and sites of preferential formation of PAH adducts along the p53 gene. Endogenously methylated CpG dinucleotides are the preferred sites for G to T transversions, accounting for more than 50% of such mutations in lung tumors. The same dinucleotide, when present within CpG-methylated mutational reporter genes, is the target of G to T transversion hotspots in cells exposed to the model PAH compound benzo[a]pyrene-7,8-diol-9,10-epoxide. As summarized here, a number of other tobacco smoke carcinogens also can cause G to T transversion mutations. The available data suggest that p53 mutations in lung cancers can be attributed to direct DNA damage from cigarette smoke carcinogens rather than to selection of pre-existing endogenous mutations.

Tobacco smoking, harm reduction, and biomarkers.

The only known way to reduce cancer risk in smokers is complete cessation, but many smokers are unable or unwilling to quit. Consequently, tobacco companies are now marketing products that purport to reduce carcinogen exposure, with the implication that such products provide a safer way to smoke. Moreover, researchers are exploring ways to reduce the amount of cigarette smoke carcinogens to which the smokers are exposed. Although these methods are, in theory beneficial, it is possible that the perceived availability of "safe" ways to smoke will cause some former smokers to resume smoking and some current smokers to delay quitting. Thus, the extent of exposure reduction and the impact on public health of these methods need to be considered carefully. However, risk reduction and its relation to exposure are not simple to estimate. The way people smoke and the way they respond to carcinogen exposure are both highly variable, as evidenced by the previous history of smokers who switched to light, or low-tar cigarettes. This can actually increase risk in some smokers. The evaluation of exposure reduction will therefore need to be multidisciplinary and include in vitro cell culture studies, animal studies, human clinical studies, and epidemiologic studies. Biomarkers will be critical for rapidly evaluating the effects of new strategies or products to reduce exposure to tobacco smoke carcinogens. No single biomarker will likely satisfy our assessment needs, and so a panel of biomarkers should be used that includes biomarkers of exposure, biologically effective dose, and potential harm. In addition, usefulness of new products will need to be tested in people of different susceptibilities (i.e., who vary in behavior, sex, age, genetics, and prior tobacco use). Even if the new products are shown to be effective at reducing lung carcinogens, they should not be used alone but rather be incorporated into a comprehensive tobacco control program.

Effects of benzyl isothiocyanate and phenethyl isothiocyanate on DNA adduct formation by a mixture of benzo[a]pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in A/J mouse lung.

Dietary phenethyl isothiocyanate (PEITC) and a mixture of dietary PEITC and benzyl isothiocyanate (BITC) inhibit lung tumorigenesis in A/J mice induced by a mixture of the tobacco smoke carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In this study, we tested the hypothesis that inhibition of tumorigenesis by these isothiocyanates was due to inhibition of DNA adduct formation. We quantified the following pulmonary DNA adducts: N2-[7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10-yl]deoxyguanosine (BPDE-N2-dG) from B[a]P; and O(6)-methylguanine (O(6)-mG) and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing adducts from NNK. Initial experiments demonstrated that there were no effects of B[a]P on NNK-DNA adduct formation, or vice versa, and established by way of a time course study the appropriate sacrifice intervals for the main experiment. Dietary PEITC, or dietary BITC plus PEITC, inhibited the formation of HPB-releasing DNA adducts of NNK at several of the time points examined. There were no effects of dietary isothiocyanates on levels of O(6)-mG or BPDE-N2-dG. These results, which are consistent with previous studies in rats and with tumor inhibition data in mice, support a role for inhibition of HPB-releasing DNA adducts of NNK as a mechanism of inhibition of tumorigenesis by dietary PEITC and BITC plus PEITC. However, the observed inhibition was modest, suggesting that other effects of isothiocyanates are also involved in chemoprevention in this model.

Maternal Cigarette Smoking, Metabolic Gene Polymorphism, and Infant Birth Weight

This study sought to clarify the relation, if any, between genetic susceptibility to cigarette smoke and adverse pregnancy outcomes. The working hypothesis was that the risk of reduced birth weight (or increased risk of low birth weight [LBW], <2500 g) is modified by maternal genetic susceptibility as defined by polymorphisms for two genes regulating the metabolism of polycyclic aromatic hydrocarbons, the most important carcinogens in tobacco smoke. A case-control study enlisted 741 women delivering live singleton infants, 567 had never smoked, whereas 174 had smoked at some time. The series included 207 preterm or LBW infants. All three possible genotypes for the CYP1A1 Mspl polymorphism (AA, homozygous wild type; Aa, heterozygous variant type; aa, homozygous variant type) were analyzed, as was the presence or absence of the GSTT1 deletion polymorphism. The mean birth weight in women who had smoked at some time in their lives was 280 g lower than for those who had never smoked, and the mean gestational age was 0.8 week shorter. The odds ratio (OR) for preterm birth was 1.8 in the smokers. Continuous smoking during pregnancy carried an OR for LBW of 2.1; the mean birth weight was reduced by 377 g compared with nonsmokers. When analyzing CYP1A1, the reduction in birth weight was 252 g for the AA genotype (OR, 1.3) and 520 g for the Aalaa genotype group (OR, 3.2). Birth weight was reduced by 285 g (OR, 1.7) when the GSTT1 was present and 642 g (OR, 3.5) when it was absent. Birth weights were most reduced, by a mean of 1285 g, in smoking mothers bearing the CYP1A1 Aalaa and GSTT1 absent genotypes. Similar effects were noted for gestational age. Genotype had no independent adverse effect on women who had never smoked. Comparable results emerged when allowing for maternal ethnicity. Maternal genotypes for enzymes participating in metabolism of polycyclic aromatic hydrocarbons alter the association between cigarette smoking and birth weight. This finding raises the question of whether metabolic genes interact with smoking, and it may in time help to identify high-risk women who might be persuaded not to smoke.