Showing papers by "Qingyi Wei published in 1996"

Reduced DNA Repair Capacity in Lung Cancer Patients

Abstract: Although lung cancer is the paradigm of a tobacco-induced malignancy, host-specific factors modulate susceptibility to tobacco carcinogenesis. Variations in DNA repair may influence the rate of removal of DNA damage and of fixation of mutations. To test the hypothesis that genetically determined DNA repair capacity (DRC) modulates lung cancer susceptibility, we conducted a pilot case-control study of 51 patients with newly diagnosed, previously untreated lung cancer and 56 controls identified from local community centers and frequency matched to the cases on age, sex, and ethnicity. The subjects were ascertained and interviewed for an ongoing molecular epidemiological investigation of lung cancer susceptibility. We measured DRC in the subjects' peripheral blood lymphocytes by using the host-cell reactivation assay, which measures cellular reactivation of a reporter gene damaged by exposure to 75 microM benzo(a)pyrene diol epoxide. The mean level of DRC in cases (3.3%) was significantly lower than that in controls (5.1%) (P < 0.01). Only nine cases (18%) had DNA repair levels greater than the median value of repair in the controls. This median level of DRC in controls was used as the cutoff value for calculating the odds ratios. After adjustment for age, sex, ethnicity, and smoking status, the cases were five times more likely than the controls to have reduced DRC (odds ratio, 5.7; 95% confidence interval, 2.1-15.7). Younger cases (< 65 years) and smokers were more likely than controls to have reduced DRC. These findings suggest that individuals with reduced DRC are at an increased risk of developing lung cancer.

Benzo (a) pyrene diol epoxide – induced chromosomal aberrations and risk of lung cancer

Abstract: Benzo(a)pyrene is considered a classic DNA-damaging carcinogen and is one of a multitude of polycyclic aromatic hydrocarbons commonly found in tobacco smoke and in the ambient environment. In this report, we describe the characteristics of chromosomal aberrations induced in vitro by activated benzo(a)pyrene diol epoxide (BPDE) in lymphocyte cultures of 172 normal individuals ages 19-95 years and present the analysis of a pilot case-control study of 33 lung cancer patients and 96 selected controls without history of cancer and frequency matched on age (50-85 years) to the cases. The BPDE-induced chromosomal aberrations were predominantly single chromatid breaks, with few isochromatid breaks or exchange figures. In the 172 normal subjects, the frequencies of both spontaneous and BPDE-induced chromatid breaks were not correlated with age, sex, ethnicity, or tobacco use. However, the frequency of BPDE-induced chromatid breaks was significantly correlated with the frequency of spontaneous chromatid breaks (r = 0.19, P < 0.05). In addition, Hispanics had significantly higher mean BPDE-induced chromatid breaks than did non-Hispanic whites (P < 0.01). From the case-control analyses, the frequency of BPDE-induced chromosomal aberrations was significantly higher in cases (mean, 0.67 breaks/cell) than in controls (mean, 0.41 breaks/cell; P < 0.0001). An adjusted odds ratio of 6.53 (95% confidence interval, 3.74-11.4) for lung cancer was associated with increased frequency of these chromosomal aberrations. The higher rate of BPDE-induced chromosomal aberrations may be due to inefficient DNA repair. These findings warrant additional molecular epidemiological studies. The BPDE mutagen sensitivity assay will facilitate epidemiological studies of genetic susceptibility to smoking-related cancers.

In Vitro Induction of Benzo(a)pyrene Diol Epoxide-DNA Adducts in Peripheral Lymphocytes as a Susceptibility Marker for Human Lung Cancer

Abstract: Given the same exposure, DNA adduct profiles can be considered as a phenotypic marker for carcinogen metabolism and DNA repair, which may reflect individual susceptibility to chemical carcinogenesis. Based on this notion, we have established a straightforward assay that measures induced DNA adducts in peripheral lymphocytes exposed in vitro to a model carcinogen, benzo(a)pyrene diol epoxide (BPDE) by 32P-postlabeling. To test the hypothesis that the levels of induced DNA adducts are a predictor for cancer risk, we conducted a pilot study of 21 lung cancer patients and 41 healthy frequency-matched controls. We found that the peripheral lymphocytes of cancer patients tended to accumulate higher levels of BPDE-DNA adducts than controls did (mean ± SE of relative adduct labeling × 107 value; 59.6 ± 12.0 versus 39.4 ± 6.1 for cases and controls, respectively; P = 0.09). Using the tertile relative adduct labeling value of controls (10 adducts/107 nucleotides) as the cutoff point, 18 of 21 cases and 23 of 41 controls distributed above this level (odds ratio, 4.7; 95% confidence interval, 1.2–18.5). In logistic regression analysis, the level of induced adduct was an independent risk factor (odds ratio, 6.4; 95% confidence interval, 1.3–29.4) after adjustment for the potential confounding factors, i.e., age, sex, ethnicity, and smoking. Stratified analyses showed that greater differences in DNA adduct levels induced by BPDE between cases and controls were observed in individuals younger than 65 years and in nonsmokers. Despite the small sample size, the significant association between the level of BPDE-induced DNA adducts and risk for lung cancer suggests that this assay is a promising method for further investigations.

DNA repair capacity correlates with mutagen sensitivity in lymphoblastoid cell lines.

Abstract: This study describes a correlation between cellular DNA repair capacity and the frequency of mutagen-induced in vitro chromosomal breaks in selected lymphoblastoid cell lines. Two assays, host cell reactivation (HCR) assay for measuring cellular DNA repair capacity and in vitro mutagen sensitivity assay, have recently been shown to be useful biomarkers for such susceptibility. Increased in vitro mutagen sensitivity, measured by the number of induced chromatid breaks, has been postulated to reflect decreased capacity of DNA repair, as measured by the HCR assay. However, these two assays have not been examined in parallel to test this hypothesis. In this study, we performed both assays in 16 established lymphoblastoid cell lines derived from patients with xeroderma pigmentosum (n = 3), ataxia telangiectasia (n = 2), head and neck cancer (n = 3), and melanoma (n = 2), and from normal human subjects (n = 6) using UV light, 4-nitroquinoline-1-oxide (4-NQO; an UV-mimetic agent), and gamma-irradiation as the test agents. The measurements from the HCR assay correlated significantly with the frequency of chromatid breaks induced by either UV irradiation (r = -0.69; P < 0.01) or 4-NQO (r = -0.70; P < 0.01). Although published data suggest that damage induced by UV and 4-NQO may be repaired by different pathways, the two agents induced similar frequencies of chromatid breaks (r = 0.68; P < 0.01) in the tested cell lines. Our results also indicated that the HCR assay is not suitable to test agents that cause DNA strand breaks, such as gamma-irradiation, whereas the mutagen sensitivity assay is. Although reduced cellular DNA repair capacity correlated with increased frequency of mutagen-induced chromatid breaks in these cell lines, these two assays have different sensitivities in measuring the repair of damage induced by different carcinogens; therefore, the use of both assays is recommended for future molecular epidemiological studies of cancer susceptibility.

Mutagen Sensitivity and Risk of Gliomas: A Case-Control Analysis

Abstract: Although the risk factors contributing to the etiology of brain tumors remain largely unknown, this pilot study suggests that genetically determined sensitivity to environmental carcinogens may play a role in the pathogenesis of these tumors. In this study, we examined short-term lymphocyte cultures from 45 adult malignant glioma patients and 117 age-, sex-, and ethnicity-matched healthy controls for mutagen-induced chromatid breaks and evaluated their family history of cancer, smoking, and demographic variables to ascertain the association between mutagen sensitivity and risk of brain tumors. The mutagen selected was γ-radiation. The mean number of induced breaks/cell was 0.72 (SD = 0.45) for the cases and 0.45 (SD = 0.35) for the controls ( P < 0.0001). Using the median number of induced breaks/cell in the controls as the breakpoint for defining mutagen sensitivity, we observed an unadjusted odds ratio of 5.36 (95% confidence interval = 2.12–13.69) for mutagen sensitivity and brain tumor risk and an adjusted odds ratio of 5.79 (2.26–14.83), when we controlled for epidemiological risk factors including smoking, race, income, and education. Although a larger study is needed to confirm this intriguing result, these preliminary findings suggest that increased sensitivity to radiation is an independent risk factor for gliomas.

Fluorescence In Situ Hybridization Method for Measuring Transfection Efficiency

Abstract: We describe here the use of fluorescence in situ hybridization (FISH) to measure the transfection efficiency of the transient expression vector pCMVcat in lymphoblasts and fibroblasts. By using a pCMVcat probe, we can visualize the location of the plasmid after transfection and thus determine transfection efficiency. In this report, we show that, for transfection of pCMVcat by the diethylaminoethyl-dextran method, the transfection efficiency was about 15 and 70 times greater in fibroblasts and lymphoblasts, respectively, when measured by the FISH method as compared to the efficiency measured by cotransfection with pCMV beta gal. Based on these results, we conclude that the FISH method is a highly sensitive, specific and direct measure of transfection efficiency of a transient expression vector and that it may be useful for evaluating laboratory assays in which the quantitative aspects of transfection and the effect of plasmid DNA damage on transfection efficiency are important.