Gender differences in genetic damage induced by the tobacco-specific nitrosamine NNK and the influence of the Thr241Met polymorphism in the XRCC3 gene

Mechanochemistry for Healthcare: Revealing the Nitroso Derivatives Genesis in the Solid State

Nitroso derivatives with unique characteristics have been extensively studied in various fields, including biology and clinical research. Although there has been substantial investigation of "nitrosable" components in many drugs and commonly consumed nutrients, there is still a need for a higher awareness about their formation and characterization. This study demonstrates how these derivatives can be produced through a mechanochemical procedure under solid-state conditions. The results include synthesizing previously unknown compounds with potential biological and pharmaceutical applications, such as a nitrosamine derived from a Diclofenac-like structure.

Use of the cytokinesis-blocked micronucleus assay to detect gender differences and genetic instability in a lung cancer case-control study

BACKGROUND

Although tobacco exposure is the predominant risk factor for lung cancer, other environmental agents are established lung carcinogens. Measuring the genotoxic effect of environmental exposures remains equivocal, as increases in morbidity and mortality may be attributed to coexposures such as smoking.

METHODS

We evaluated genetic instability and risk of lung cancer associated with exposure to environmental agents (e.g., exhaust) and smoking among 500 lung cancer cases and 500 controls using the cytokinesis-blocked micronucleus (CBMN) assay. Linear regression was applied to estimate the adjusted means of the CBMN endpoints (micronuclei and nucleoplasmic bridges). Logistic regression analyses were used to estimate lung cancer risk and to control for potential confounding by age, gender, and smoking.

RESULTS

Cases showed significantly higher levels of micronuclei and nucleoplasmic bridges as compared with controls (mean ± SEM = 3.54 ± 0.04 vs. 1.81 ± 0.04 and mean ± SEM = 4.26 ± 0.03 vs. 0.99 ± 0.03, respectively; P < 0.001) with no differences among participants with or without reported environmental exposure. No differences were observed when stratified by smoking or environmental exposure among cases or controls. A difference in lung cancer risk was observed between nonexposed male and female heavy smokers, although it was not statistically significant (I(2) = 64.9%; P value for Q statistic = 0.09).

CONCLUSIONS

Our study confirms that the CBMN assay is an accurate predictor of lung cancer and supports the premise that heavy smoking may have an effect on DNA repair capacity and in turn modulate the risk of lung cancer.

IMPACT

Identifying factors that increase lung cancer risk may lead to more effective prevention measures.

[Adverse birth outcomes of maternal smoking during pregnancy and genetic polymorphisms: exploiting gene-environment interaction]

It has been recognized that metabolic enzymes mediating genetic susceptibility to environmental chemicals such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls might be related to adverse human health. Recent studies, including the Hokkaido Study of Environmental and Children's Health, have shown that metabolic enzymes mediating genetic susceptibility to environmental chemicals including tobacco smoke might be related to adverse birth outcomes. Certain maternal genetic polymorphisms in the polycyclic aromatic hydrocarbons (PAHs)-metabolizing enzymes have been shown to enhance the association between maternal smoking and infant birth weight in both Caucasians and Japanese. For maternal genetic polymorphisms encoding the N-nitrosamine-metabolizing enzymes, we found that infant birth weight, birth length and birth head circumference were significantly smaller among infants of smokers than among those of nonsmokers and quitters. The adverse effects of maternal smoking on infant birth size may be modified by maternal genetic polymorphisms. Further study is required to clarify the potential association between genetic polymorphisms and cognitive function in childhood, becauae it has been reported that a small birth length or a small head circumference at birth might affect neurobehavioral development during early childhood. It is necessary to elucidate additive impacts of genetic factors on adverse effects of various chemicals commonly encountered in our daily lives, follow up the development of children, and carry out longitudinal observation.

Evaluating the effects of genetic variants of DNA repair genes using cytogenetic mutagen sensitivity approaches

Mutagen sensitivity, measured in short-term cultures of peripheral blood lymphocytes by cytogenetic endpoints, is an indirect measure for DNA repair capacity and has been used for many years as a biomarker for intrinsic susceptibility for cancer. In this article, we briefly give an overview of the different cytogenetic mutagen sensitivity approaches that have been used successfully to evaluate the biological effects of polymorphisms in DNA repair genes based on a current review of the literature and based on the need for biomarkers that would allow the characterization of the biological and functional significance of such polymorphisms. We also address some of the future challenges facing this emerging area of research.

Variants in folate pathway genes as modulators of genetic instability and lung cancer risk

Genetic instability plays a crucial role in cancer development. The genetic stability of the cell as well as DNA methylation status could be modulated by folate levels. Several studies suggested associations between polymorphisms in folate genes and alterations in protein expression and variations in serum levels of the folate. The objective of this study was to investigate the effect of folate pathway polymorphisms on modulating genetic instability and lung cancer risk. Genotyping of 5 SNPs in folate pathway genes and cytokinesis-blocked micronucleus cytome assay analysis (to determine the genetic instability at baseline and following NNK treatment) was conducted on 180 lung cancer cases and 180 age-, gender-, and smoking-matched controls. Our results showed that individually, folate pathway SNPs were not associated with cytogenetic damage or lung cancer risk. However, in a polygenic disease such as lung cancer, gene-gene interactions are expected to play an important role in determining the phenotypic variability of the diseases. We observed that interactions between MTHFR677, MTHFR1298, and SHMT polymorphisms may have a significant impact on genetic instability in lung cancer patients. With regard to cytogenetic alterations, our results showed that lymphocytes from lung cancer patients exposed to the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone [NNK] had considerably increased frequency of cytogenetic damage in presence of MTHFR 677, MTHFR 1298, and SHMT allelic variants. These findings support the notion that significant interactions may potentially modulate the lung cancer susceptibility and alter the overall the repair abilities of lung cancer patients when exposed to tobacco carcinogens such as NNK.

XRCC3 Thr241Met polymorphism with lung cancer and bladder cancer: a meta-analysis

Several studies have investigated the associations between X-ray repair cross-complementing group 3 (XRCC3) Thr241Met polymorphism and the susceptibility to lung cancer and bladder cancer, but results have been inconclusive. In order to derive a more precise estimation of the relationship, a meta-analysis was performed. A total of 22 case control studies, including 2976 cases and 4495 controls for lung cancer, and 3445 cases and 4599 controls for bladder cancer, met the inclusion criteria and were selected. Overall, there was no evidence showing a significant association between XRCC3 Thr241Met polymorphism and lung cancer risk. Furthermore, the results for bladder cancer showed that significant decreased risk was found for the additive model (odds ratio [OR] = 0.959, 95% confidence interval [CI], 0.924-0.996) and dominant model (OR = 0.982, 95% CI, 0.963-1.000) but not for the recessive model (OR = 0.958, 95% CI, 0.905-1.014). In summary, our meta-analysis indicates that XRCC3 Thr241Met polymorphism may be weakly associated with the risk of bladder cancer. (Cancer Sci 2010).

Cytokinesis-blocked micronucleus cytome assay biomarkers identify lung cancer cases amongst smokers

The multi-endpoint cytokinesis-blocked micronucleus assay is used for assessing chromosome aberrations. We have recently reported that this assay is extremely sensitive to genetic damage caused by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and that the binucleated cells with micronuclei, nucleoplasmic bridges, and nuclear buds in lymphocytes (chromosome damage endpoints measured by the assay) are strong predictors of lung cancer risk. In the current study, we refined our analysis to include toxicity endpoints (micronuclei in mononucleated cells, apoptosis, necrosis, and nuclear division index) to investigate the benefit of including these variables on improving the predictive value of the assay. Baseline and NNK-induced micronuclei in mononucleated cells were significantly higher in patients (n = 139) than controls (n = 130; P < 0.001). Baseline apoptosis was higher among cases; however, the controls showed a significant higher fold increase in NNK-induced apoptosis compared with baseline (P < 0.001). Principal components analysis was used to derive a summary measure for all endpoints and calculate the positive predictive value (PPV) and negative predictive value (NPV) for disease status. First principal component for NNK-induced chromosome damage endpoints (binucleated cells with micronuclei, nucleoplasmic bridges, and nuclear buds) had an area under the curve = 97.9 (95% confidence interval, 95.9-99.0), PPV = 94.8, and NPV = 92.6. The discriminatory power improved when micronuclei in mononucleated cells were included: area under the curve = 99.1 (95% confidence interval, 97.9-100.0), PPV = 98.7 and NPV = 95.6. The simplicity, rapidity, and sensitivity of the assay together with potential for automation make it a valuable tool for screening and prioritizing potential cases for intensive screening.

Cigarette smoking and lung cancer: modeling effect modification of total exposure and intensity

BACKGROUND

A recent analysis indicates that the excess odds ratio for lung cancer by smoking is described by a function that is linear in pack-years and exponential in the logarithm of smoking intensity and its square (Cancer Epidemiol Biomarkers Prev. 2006;15:517-523). The model suggests that below 15-20 cigarettes per day there is a "direct exposure rate" effect, ie, the excess odds ratio per pack-year for higher intensity (and shorter duration) smokers is greater than for lower-intensity (and longer duration) smokers. Above 20 cigarettes per day, there is an "inverse-exposure-rate" effect, ie, the excess odds ratio per pack-year for higher intensity smokers is smaller than for lower-intensity smokers.

METHODS

Using pooled data from 2 large case-control studies of lung cancer (the European Smoking and Health Study and the German Radon Study), we evaluated effect modification of the association between smoking and lung cancer.

RESULTS

Interaction effects are very specific. Variations in risk of lung cancer with years since cessation of smoking, age, method of inhalation, and type of cigarette result from interactions with smoking intensity, and not total pack-years. In contrast, risk variations by sex result from the interaction with total pack-years, while intensity effects are homogeneous. Risk variations by age at which smoking started result from interactions with both total pack-years and intensity. All intensity interactions are homogeneous across studies.

CONCLUSIONS

The specificity of the interactions may provide clues for the molecular basis of the smoking and lung cancer relationship.

Influence of glutathione S-transferase polymorphisms on genotoxic effects induced by tobacco smoke

Genotoxicity of tobacco smoke has long been investigated and tobacco smoke is considered to be one of the principal human carcinogens. Although its role in DNA-damage induction and cancer development has been documented, the mechanisms by which this happens are not well understood. Many chemical constituents of tobacco smoke are enzymatically metabolized by phase-I and phase-II enzymes, but modifications in coding and regulating sequences of these genes could influence their ability to detoxify these compounds. In this work, we studied several enzymes involved in the metabolism of xenobiotics, viz. the glutathione S-transferases (GST) M1, T1, P1 and A1, with respect to their influence on the genotoxic effects induced by cigarette smoking. We assessed the genotoxic effects of tobacco smoke on peripheral blood lymphocytes of 72 healthy caucasians by use of the chromosomal aberration (CA) assay and the micronucleus (MN) test. Genotypes of GST M1, T1, P1 and A1 were determined by means of the polymerase chain reaction and methods based on restriction fragment length polymorphism (RFLP). We found that smoke and gender are the two variables that most influence the DNA damage. In particular, we observed that female smokers seem to be more sensitive than male smokers, having a significantly higher frequency of CAs. Moreover, a significant increase in frequency of micronuclei in bi-nucleated cells (BNMN) was found in smokers, but not in non-smokers. This increase seems to be influenced not only by age and gender, but also by genetic constitution. Subjects carrying GSTM1-null genotype seemed to have an higher susceptibility to DNA damage induced by tobacco smoke than GSTM1-positive ones. When considering a combination of GST genotypes, we found a lower BNMN frequency in subjects with GSTP1 variant allele plus GSTM1-positive genotypes, while the most damaged cells are found in subjects bearing GSTM1-null plus GSTP1-wild type. Our results suggest that investigation of the association between several gene polymorphisms and important endpoints of DNA damage could contribute to better understanding the role of gene-gene interaction.

Gene-environment interactions between smoking and a haplotype of RAI, ASE-1 and ERCC1 polymorphisms among women in relation to risk of lung cancer in a population-based study

Homozygous carriers of a haplotype consisting of ERCC1 Asn118Asn(A), ASE-1 G-21A(G), RAI IVS1 A4364G(A) are at increased risk of lung cancer especially among women. Here, we analyse for gene-environment interactions with the predefined haplotype in a case cohort study including 428 lung cancer cases and a comparison group of 800 persons, all from the prospective Diet, Cancer and Health cohort of 57,000 Danes. At high smoking intensity (>20g tobacco/day), there was only additional risk of smoking intensity among women who were homozygous carriers of the haplotype (IRR=2.03; 95% CI: 1.10-3.73 per 5 additional g tobacco/day).

Influence of DNA repair gene polymorphisms of hOGG1, XRCC1, XRCC3, ERCC2 and the folate metabolism gene MTHFR on chromosomal aberration frequencies

We have studied the effect of genetic polymorphisms in the DNA repair genes hOGG1, XRCC1, XRCC3, ERCC2 and the MTHFR gene in the folate metabolism on the frequencies of cells with chromosomal aberrations (CA), chromosome-type aberrations (CSA), chromatid-type aberrations (CTA), chromatid breaks (CTB) and chromatid gaps (CTG) scored in peripheral blood lymphocytes from 651 Norwegian subjects of Caucasian descendant. DNA was extracted from fixed cell suspensions. The log-linear Poisson regression model was used for the combined data which included age, smoking, occupational exposure and genotype for 449 subjects. Our results suggest that individuals carrying the hOGG1 326Cys or the XRCC1 399Gln allele have an increased risk of chromosomal damage, while individuals carrying the XRCC1 194Trp or the ERCC2 751Gln allele have a reduced risk regardless of smoking habits and age. Individuals carrying the XRCC1 280His allele had an increased risk of CSA which was only apparent in non-smokers. This was independent of age. A protective effect of the XRCC3 241Met allele was only found in the older age group in non-smokers for CA, CSA and CTA, and in smokers for CSA. In the youngest age group, the opposite effect was found, with an increased risk for CA, CTA and CTG in smokers. Carrying the MTHFR 222Val allele gave an increased risk for chromosome and chromatid-type aberrations for both non-smokers and smokers, especially for individuals in the older age group, and with variable results in the youngest age group. The variables included in the different regression models accounted, however, for only 4-10% of the variation. The frequency ratio for CTG was significantly higher than for CTA and CTB for only 7 of the 43 comparisons performed. Some of the gap frequencies diverge from the trend in the CA, CSA, CTA and CTB results.

Cytokinesis-blocked micronucleus assay as a novel biomarker for lung cancer risk

In this case-control study, we modified the cytokinesis-block micronucleus (CBMN) assay, an established biomarker for genomic instability, to evaluate susceptibility to the nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by measuring the frequency of NNK-induced chromosomal damage endpoints (micronuclei, nucleoplasmic bridges, and nuclear buds) per 1,000 binucleated lymphocytes. Spontaneous and NNK-induced chromosomal damage were significantly higher in lung cancer patients compared with controls. Forty-seven percent of cases (versus 12% of controls) had >or=4 spontaneous micronuclei, 66% of cases (and no controls) had >or=4 spontaneous nucleoplasmic bridges, and 25% of cases (versus 5% of controls) had >or=1 spontaneous nuclear bud (P < 0.001). Similarly, 40% of cases (versus 6% of the controls) had >or=5 NNK-induced micronuclei, 89% of cases (and no controls) had >or=6 induced nucleoplasmic bridges, and 23% of cases (versus 2% of controls) had >or=2 induced nuclear buds (P < 0.001). When analyzed on a continuous scale, spontaneous micronuclei, nucleoplasmic bridges, and nuclear buds were associated with 2-, 29-, and 6-fold increases in cancer risk, respectively. Similarly, NNK-induced risks were 2.3-, 45.5-, and 10-fold, respectively. We evaluated the use of CBMN assay to predict cancer risk based on the numbers of micronuclei, nucleoplasmic bridges, and nuclear buds defined by percentile cut points in controls. Probabilities of being a cancer patient were 96%, 98%, and 100% when using the 95th percentiles of spontaneous and NNK-induced micronuclei, nucleoplasmic bridges, and nuclear buds, respectively. Our study indicates that the CBMN assay is extremely sensitive to NNK-induced genetic damage and may serve as a strong predictor of lung cancer risk.