32P-postlabeling analysis of DNA adducts in different populations

Bulky DNA Adducts, Tobacco Smoking, Genetic Susceptibility, and Lung Cancer Risk

The generation of bulky DNA adducts consists of conjugates formed between large reactive electrophiles and DNA-binding sites. The term "bulky DNA adducts" comes from early experiments that employed a ³²P-DNA postlabeling approach. This technique has long been used to elucidate the association between adducts and carcinogen exposure in tobacco smoke studies and assess the predictive value of adducts in cancer risk. Molecular data showed increased DNA adducts in respiratory tracts of smokers vs nonsmokers. Experimental studies and meta-analysis demonstrated that the relationship between adducts and carcinogens was linear at low doses, but reached steady state at high exposure, possibly due to metabolic and DNA repair pathway saturation and increased apoptosis. Polymorphisms of metabolic and DNA repair genes can increase the effects of environmental factors and confer greater likelihood of adduct formation. Nevertheless, the central question remains as to whether bulky adducts cause human cancer. If so, lowering them would reduce cancer incidence. Pooled and meta-analysis has shown that smokers with increased adducts have increased risk of lung cancer. Adduct excess in smokers, especially in prospective longitudinal studies, supports their use as biomarkers predictive of lung cancer.

Induced minisatellite germline mutations in herring gulls (Larus argentatus) living near steel mills

Despite widespread industrial release of genotoxic contaminants, little is understood of their role in inducing germline mutations in natural populations. We used multilocus DNA fingerprinting to quantify germline minisatellite mutations in families of herring gulls (Larus argentatus) in three nesting categories: (a) near cities with large steel mills operating coking ovens; (b) near cities without steel mills; and (c) in rural locations removed from point sources of contamination. Gulls nesting near integrated steel mills showed significantly higher mutation rates than gulls from rural locations (Fisher's exact, P=0.0004); urban sites without steel mills fell midway between steel and rural sites (difference from rural; Fisher's exact, P=0.19). Distance of the nesting location of herring gulls from the steel industries' coking ovens was negatively correlated with minisatellite mutation rate demonstrating significant risk for induced germline mutations in cities with steel operations (Kendall Tau; tau=0.119; P<0.0001).

Benzo[a]pyrene diol-epoxide DNA adducts and levels of polycyclic aromatic hydrocarbons in autoptic samples from human lungs

Benzo[a]pyrene (BaP) and other polycyclic aromatic hydrocarbons (PAHs) which are present in cigarette smoke, are common air and food genotoxic contaminants and possible human carcinogens. We measured the following PAH levels: benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, BaP, dibenzo[a,h]anthracene, benzo[g,h,i]perylene as well as (+/-) syn and anti BaP diol-epoxide (BPDE) DNA adducts in autopsy samples from the lungs of non-smokers, ex-smokers and smokers who had lived in Florence, Italy. PAH levels in lung tissue were similar in all groups, with the exception of dibenzo[a,h]anthracene (DBA), which was higher in lung samples from smokers (n = 10, 0.18+/-0.17 ng/g d.w, mean +/- S.D.) compared to non-smokers (n = 15, 0.046+/-0.025 ng/g d.w) (P < 0.05), whereas ex-smokers (n = 5), had intermediate levels (0.07+/-0.03 ng/g d.w). The average level of total BPDE-DNA adducts was 4.46+/-5.76 per 10(8) bases in smokers, 4.04+/-2.37 per 10(8) in ex-smokers and 1.76+/-1.69 per 10(8) in non-smokers. The levels of non-smokers were significantly different (P < 0.05) from the levels of the smokers and ex-smokers combined. Total BPDE-DNA adducts were correlated with BaP levels in the lung samples in which both determinations were obtained (r = 0.63). Our results demonstrate that the biological load of PAHs due to environmental pollution is similar in individuals who smoke and those who do not, but BPDE-DNA adducts are higher in smokers and ex-smokers compared to non-smokers. This study further confirms the usefulness of BPDE-DNA adduct levels determination in the lungs from autopsy samples for monitoring long-term human exposure to BaP, a representative PAH.

Coke oven workers study: the effect of exposure and GSTM1 and NAT2 genotypes on DNA adduct levels in white blood cells and lymphocytes as determined by 32P-postlabelling

The DNA adduct levels in total white blood cells (WBC) and lymphocytes (LYM) isolated from the blood of the same individuals were evaluated using the 32P-postlabelling assay for bulky aromatic adducts. In this study, 68 male coke oven workers and 56 machines workers as a matched control were enrolled. Personal monitors were used to evaluate exposure to eight carcinogenic PAHs, including B[alpha]P, during an 8-h working shift. The exposure among coke even workers ranged widely from 0.6 to 547 micrograms/m3 and from 2 to 62,107 ng/m3, for carcinogenic PAHs and B[alpha]P, respectively. The respective values in controls were from 0.07-1.64 microgram/m3 and from 1-63 ng/m3. A significant correlation between WBC- and LYM-DNA adduct levels was found (r = 0.591, P < 0.001). DNA adduct levels in both WBC and LYM were significantly elevated in coke oven workers as compared with controls, but adduct levels were generally low (WBC: medians 2.61 vs. 1.83 LYM: 2.47 vs. 1.65 adducts/10(8) nucleotides). LYM-DNA adduct levels were significantly higher for smokers as compared with nonsmokers in both the exposed and control groups. No such differences in WBC-DNA adduct levels were observed. Positive significant correlations were found at the individual level between DNA adducts in both cell types and carcinogenic PAHs and/or B[alpha]P in the inhaled air (r = 0.38-0.45, P < 0.001). A significant correlation at the individual level between LYM-DNA adducts and urinary cotinine was also observed (r = 0.37, P < 0.001). No differences in DNA adduct levels could be attributed to GSTM1 or NAT2 genotype in either group. Nor was there any clear association of DNA adduct levels with combined GSTM1/NAT2 genotypes. The effect of personal exposure to carcinogenic PAHs on DNA adduct levels in both cell types was also investigated using a logistic regression model with adjustment for possible modulating effect of confounders (smoking, GSTM1, NAT2, age, plasma levels of vitamins A and E, body mass index and diet). The results showed that coke oven workers had a significantly (P < 0.05) increased adjusted Odds Ratio (OR = 4.2 and 3.9 for WBC and LYM-DNA adducts) for occurrence of higher DNA adduct levels as compared to controls. The results also showed that the relative risk of an increased prevalence of 'abnormal' values of DNA adduct levels was exposure-dose related. The influence of confounding variables was found not to be significant in this study of relatively limited size. In spite of this, the results suggest that the DNA adduct levels in LYM seem to be affected by smoking (OR = 1.8 for smokers) and are modulated by the influence of NAT2 genotypes (OR = 1.6 for slow acetylators). Our findings indicate that both cell types are generally suitable to monitor occupational exposure to PAHs, and the results suggest that coke oven workers, smoking individuals and slow acetylators sustain more genetic damage in their LYM-DNA from exposure to carcinogenic PAHs than individuals without these actors.

The molecular epidemiology of lung cancer

One in ten tobacco smokers develops bronchogenic carcinoma over a lifetime. The study of susceptibility of an individual and a population to lung cancer traditionally has been limited to the study of tobacco smoke dose and family history of cancer. New insights into lung carcinogenesis have made the study of molecular markers of risk possible in human populations in the emerging field of molecular epidemiology. This review summarizes data addressing the relationships of human lung cancer to polymorphisms of phase I procarcinogen-activating and phase II-deactivating enzymes and intermediate biomarkers of DNA mutation, such as DNA adducts, oncogene and tumor suppressor gene mutation, and polymorphisms. These parameters are reviewed as they relate to tobacco smoke exposure, procarcinogen metabolizing polymorphisms, and the presence of lung cancer. Problem areas in biomarker validation, such as cross-sectional data interpretation; tissue source, race, statistical power, and ethical implications are addressed.

Methods for predicting carcinogenic hazards: new opportunities coming from recent developments in molecular oncology and SAR studies

Without epidemiological evidence, and prior to either short-term tests of genotoxicity or long-term tests of carcinogenicity in rodents, an initial level of information about the carcinogenic hazard of a chemical that perhaps has been designed on paper, but never synthesized, can be provided by structure-activity relationship (SAR) studies. Herein, we have reviewed the interesting strategies developed by human experts and/or computerized approaches for the identification of structural alerts that can denote the possible presence of a carcinogenic hazard in a novel molecule. At a higher level of information, immediately below epidemiological evidence, we have discussed carcinogenicity experiments performed in new types of genetically engineered small rodents. If a dominant oncogene is already mutated, or if an allele of a recessive oncogene is inactivated, we have a model animal with (n-1) stages in the process of carcinogenesis. Both genotoxic and receptor-mediated carcinogens can induce cancers in 20-40% of the time required for classical murine strains. We have described the first interesting results obtained using these new artificial animal models for carcinogenicity studies. We have also briefly discussed other types of engineered mice (lac operon transgenic mice) that are especially suitable for detecting mutagenic effects in a broad spectrum of organs and tissues and that can help to establish mechanistic correlations between mutations and cancer frequencies in specific target organs. Finally, we have reviewed two complementary methods that, while obviously also feasible in rodents, are especially suitable for biomonitoring studies. We have illustrated some of the advantages and drawbacks related to the detection of DNA adducts in target and surrogate tissues using the 32P-DNA postlabeling technique, and we have discussed the possibility of biomonitoring mutations in different human target organs using a molecular technique that combines the activity of restriction enzymes with polymerase chain reaction (RFLP/PCR). Prediction of carcinogenic hazard and biomonitoring are very wide-ranging areas of investigation. We have therefore selected five different subfields for which we felt that interesting innovations have been introduced in the last few years. We have made no attempt to systematically cover the entire area: such an endeavor would have produced a book instead of a review article.

A comparative investigation of DNA adducts, DNA strand breaks and gene mutations induced by benzo[a]pyrene and (+/-)-anti-benzo[a]pyrene-7,8-diol 9,10-oxide in cultured human cells

Genotoxic effects of benzo[a]pyrene (BP) and its reactive metabolites (+/-)-anti-benzo[a]pyrene-7,8-diol 9,10-oxide ((+/-)-anti-BPDE) were comparatively investigated in vitro with the permanent human fibroblast cell line MRC5CV1. Induced DNA adducts were measured by 32P-postlabeling, DNA strand breakage was determined by the comet assay and the HPRT gene mutation test was used to detect cytotoxicity and mutagenicity. Treatment of MRC5CV1 cells with S9 mix-activated BP or with (+/-)-anti-BPDE resulted in a concentration-dependent increase in DNA adducts and strand breaks. Genotoxic effects of BP and (+/-)-anti-BPDE were detected by 32P-postlabeling and the comet assay with similar sensitivity. However, under the same experimental conditions, a clear induction of gene mutations was only found after (+/-)-anti-BPDE treatment. The relationship between the induction of primary DNA alterations like DNA strand breaks and DNA adducts and the induction of gene mutations is discussed.

DNA single strand breakage, DNA adducts, and sister chromatid exchange in lymphocytes and phenanthrene and pyrene metabolites in urine of coke oven workers

OBJECTIVES

To investigate the specificity of biological monitoring variables (excretion of phenanthrene and pyrene metabolites in urine) and the usefulness of some biomarkers of effect (alkaline filter elution, 32P postlabelling assay, measurement of sister chromatid exchange) in workers exposed to polycyclic aromatic hydrocarbons (PAHs).

METHODS

29 coke oven workers and a standardised control group were investigated for frequencies of DNA single strand breakage, DNA protein cross links (alkaline filter elution assay), sister chromatid exchange, and DNA adducts (32P postlabelling assay) in lymphocytes. Phenanthrene and pyrene metabolites were measured in 24 hour urine samples. 19 different PAHs (including benzo(a)pyrene, pyrene, and phenanthrene) were measured at the workplace by personal air monitoring. The GSTT1 activity in erythrocytes and lymphocyte subpopulations in blood was also measured.

RESULTS

Concentrations of phenanthrene, pyrene, and benzo(a)pyrene in air correlated well with the concentration of total PAHs in air; they could be used for comparisons of different workplaces if the emission compositions were known. The measurement of phenanthrene metabolites in urine proved to be a better biological monitoring variable than the measurement of 1-hydroxypyrene. Significantly more DNA strand breaks in lymphocytes of coke oven workers were found (alkaline filter elution assay); the DNA adduct rate was not significantly increased in workers, but correlated with exposure to PAHs in a semiquantitative manner. The number of sister chromatid exchanges was lower in coke oven workers but this was not significant; thus counting sister chromatid exchanges was not a good variable for biomonitoring of coke oven workers. Also, indications for immunotoxic influences (changes in lymphocyte subpopulations) were found.

CONCLUSIONS

The measurement of phenanthrene metabolites in urine seems to be a better biological monitoring variable for exposure to PAHs than measurement of hydroxypyrene. The alkaline filter elution assay proved to be the most sensitive biomarker for genotoxic damage, whereas the postlabelling assay was the only one with some specificity for DNA alterations caused by known compounds.