Contribution of hMTH1 to the maintenance of 8-oxoguanine levels in lung DNA of non-small-cell lung cancer patients.

BACKGROUND: The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG-excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non-small-cell lung cancer patients. METHODS: We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided. RESULTS: The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/10(6) G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively). CONCLUSIONS: Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.

Products of oxidative DNA damage and repair as possible biomarkers of susceptibility to lung cancer.

The broad spectrum of oxidative DNA damage biomarkers [urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OH-dGuo) and 8-hydroxyguanine (8-OH-Gua)] and the level of oxidative DNA damage and repair in leukocytes DNA were analyzed in three groups of subjects: (a) lung cancer patients [all smokers (n = 51)]; (b) healthy smokers with comparable smoking status (n = 26); and (c) healthy nonsmokers (n = 38). The mean level of 8-OH-Gua in urine samples of 38 healthy nonsmokers reached a value of 1.783 +/- 0.785 nmol/day/kg. This level was significantly lower than that in the urine of the two smoker groups (cancer patients and healthy smokers), in whom the levels reached values of 2.319 +/- 1.271 and 2.824 +/- 0.892 nmol/day/kg, respectively. Urinary excretion of 8-OH-dGuo was similar in all groups of subjects. The level of 8-OH-dGuo in DNA isolated from leukocytes of cancer patients was significantly higher than that in DNA isolated from the group of healthy smokers and nonsmokers (9.44 +/- 4.77 versus 7.20 +/- 2.83 and 5.88 +/- 2.47 molecules/10(6) deoxyguanosine, respectively). Repair activity of 8-OH-Gua, as estimated by the nicking assay, was significantly higher in blood leukocytes of healthy volunteers (44.6 +/- 20.21 and 37.54 +/- 13.43 pmol/h/mg protein for smokers and nonsmokers, respectively) than in the leukocytes of lung cancer patients (24.56 +/- 11.28 pmol/h/mg protein). Because oxidative DNA insult represented by urinary excretion of oxidative DNA lesions was similar in both groups of subjects with similar smoking status, it appears likely that a higher rate of generation of oxidative damage in cellular DNA of lung cancer patients is a result of deficiency of the repair mechanism(s) in this group.

Decreased repair activities of 1,N(6)-ethenoadenine and 3,N(4)-ethenocytosine in lung adenocarcinoma patients.

To assess the role of oxidative stress and lipid peroxidation (LPO) in the pathogenesis of lung cancer, we measured the levels of 1,N(6)-ethenoadenine (epsilonA) and 3,N(4)-ethenocytosine (epsilonC) in the DNA by immunoaffinity/(32)P postlabeling (33 cases). We also measured the capacity for epsilonA and epsilonC repair (by the nicking assay) in normal and tumor lung tissues, as well as in blood leukocytes of lung cancer patients (56 cases). Repair activities for epsilonA and epsilonC were also assayed in leukocytes of healthy volunteers, matched with cancer patients for age, sex, and smoking habit (25 individuals). Up to 10-fold variations among individuals were observed both in adducts level and repair activities. No differences in epsilonA and epsilonC levels between tumor and nonaffected lung tissues were recorded. However, leukocytes accumulated a significantly higher number of DNA adducts than the lung tissues. Repair activities for both epsilonA and epsilonC were significantly higher in tumor than in normal lung tissue. No significant differences in epsilonA and epsilonC repair activities were associated with age, sex, or smoking habit. However, a significant difference in repair capacity was observed between two histological types of lung cancer, squamous cell carcinoma (SQ) and adenocarcinoma (AD). In individuals suffering from lung AD, epsilonA- and epsilonC-repair activities in normal lung and blood leukocytes were significantly lower than in SQ patients. Moreover, in nonaffected lung tissue of AD patients, the ratio epsilonA/epsilonC adducts was lower than in SQ patients. Differences have also been found between epsilonA and epsilonC repair activities of cancer patients and healthy volunteers. Repair capacity for epsilonA was significantly lower in blood leukocytes of lung cancer patients than in leukocytes of healthy volunteers (P = 0.012). This difference was even larger between healthy volunteers and patients developing inflammation-related AD (P = 0.00033). Repair activities for epsilonC were the same in leukocytes of healthy controls, all lung cancer patients, and SQ patients. However, individuals with ADs revealed significantly lower epsilonC-repair activity (P = 0.013). These results suggest that oxidative stress-mediated lipid peroxidation might contribute to induction and/or progression of lung cancer. Decreased activity of base excision repair pathway for epsilonA and epsilonC is associated particularly with inflammation-related lung AD.