Lung carcinogenesis and formation of 8-hydroxy-deoxyguanosine in mice by diesel exhaust particles

Estrogenic Activities of Nitrophenols in Diesel Exhaust Particles1

We recently isolated 3-methyl-4-nitrophenol (4-nitro-m-cresol; PNMC) and 4-nitro-3-phenylphenol (PNMPP) from diesel exhaust particles (DEP) and identified them as vasodilators. Because these compounds are alkylphenolic derivatives that might mimic hormones, we evaluated their estrogenic activity by using recombinant yeast screens, myometrial contractility assays, and in vivo uterotrophic assays. Recombinant yeast screen assays showed that both PNMC and PNMPP possess estrogenic activity. Furthermore, ovariectomized 25-day-old immature female rats injected with PNMC and PNMPP subcutaneously for 2 days showed significant increases in uterine weight among those receiving 100 mg/kg PNMC and 0.1 and 1.0 mg/kg PNMPP. To clarify further the estrogenic activity of PNMC and PNMPP, rat uterine horns were monitored in organ bath chambers for myometrial contractility in response to oxytocin (OT). Significant differences occurred in the initial and maximum contractilities to OT at 0.25 and 25 mIU/ml in uterine horns obtained from animals treated with 100 mg/kg PNMC and in the maximum contractilities to OT at 0.025, 0.25, and 25 mIU/ml in those from rats treated with 0.1 mg/kg PNMPP. These results clearly demonstrated that PNMC and PNMPP in DEP have estrogenic activity both in vitro and in vivo and might therefore be considered as endocrine-disrupting chemicals.

Oxidative damage to nuclear DNA in hyperthyroid rat liver: inability of vitamin C to prevent the damage

The effects of hyperthyroidism on oxidative DNA damage in liver tissue and modification by vitamin C supplementation were investigated in rats. Animals were rendered hyperthyroid by administration of L-thyroxine (0.4 mg/100 g food) for 25 d. In the plasma samples, T(3), T(4), and thyroid-stimulating hormone (TSH) were measured by radioimmunoassay and ascorbate spectrophotometrically. Oxidative damage to hepatic nuclear DNA was determined by measuring deoxy-guanosine (dG) and 8-oxodG by high-performance liquid chromatography with diode array detector electrochemical detection (HPLC-DAD-ECD). In hyperthyroidism, 8-oxodG/(10(5) dG) levels were significantly higher and plasma vitamin C levels lower than in control rats. The results of this experimental study show that oxidative damage to hepatic nuclear DNA increases in the hyperthyroid state and that vitamin C was not effective in preventing this damage.

Linking exposure to environmental pollutants with biological effects

Exposure to ambient air pollution has been associated with cancer. Ambient air contains a complex mixture of toxics, including particulate matter (PM) and benzene. Carcinogenic effects of PM may relate both to the content of PAH and to oxidative DNA damage generated by transition metals, benzene, metabolism and inflammation. By means of personal monitoring and biomarkers of internal dose, biologically effective dose and susceptibility, it should be possible to characterize individual exposure and identify air pollution sources with relevant biological effects. In a series of studies, individual exposure to PM(2.5), nitrogen dioxide (NO(2)) and benzene has been measured in groups of 40-50 subjects. Measured biomarkers included 1-hydroxypyrene, benzene metabolites (phenylmercapturic acid (PMA) and trans-trans-muconic acid (ttMA)), 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in urine, DNA strand breaks, base oxidation, 8-oxodG and PAH bulky adducts in lymphocytes, markers of oxidative stress in plasma and genotypes of glutathione transferases (GSTs) and NADPH:quinone reductase (NQO1). With respect to benzene, the main result indicates that DNA base oxidation is correlated with PMA excretion. With respect to exposure to PM, biomarkers of oxidative damage showed significant positive association with the individual exposure. Thus, 8-oxodG in lymphocyte DNA and markers of oxidative damage to lipids and protein in plasma associated with PM(2.5) exposure. Several types of DNA damage showed seasonal variation. PAH adduct levels, DNA strand breaks and 8-oxodG in lymphocytes increased significantly in the summer period, requiring control of confounders. Similar seasonal effects on strand breaks and expression of the relevant DNA repair genes ERCC1 and OGG1 have been reported. In the present setting, biological effects of air pollutants appear mainly related to oxidative stress via personal exposure and not to urban background levels. Future developments include personal time-resolved monitors for exposure to ultrafine PM and PM(2.5,) use of GPS, as well as genomics and proteomics based biomarkers.

Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine in rat lung DNA following subchronic inhalation of carbon black

Chronic high-dose inhalation of carbon black (CB) can produce carcinomas in rat lungs. The mechanisms underlying this response are uncertain. It has been hypothesized that chronic inflammation and cell proliferation may play a role in the development of tumors after high dose, long-term contact of the particles with lung epithelial cells. In this investigation, we analyzed the formation of a known mutagenic lesion [8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG)] in the lung DNA of rats following subchronic inhalation of CB (Printex-90 and Sterling V). Briefly, female Fischer 344 rats were exposed for 6 h/day, 5 days/week for 13 weeks to 1, 7, and 50 mg/m(3) of Printex-90 (16 nm; specific surface area 300 m(2)/g) and to 50 mg/m(3) of Sterling V CB (70 nm; surface area of 37 m(2)/g). The exposure concentration of Sterling V was selected to be equivalent in terms of retained mass in the lung to the high dose of Printex-90 at the end of exposure. However, in terms of retained particle surface area, the retained lung dose of Sterling V was equivalent to the mid-dose of Printex 90. This design allows comparison of results on the basis of retained particle mass as well as retained particle surface area between the two CB particles. The formation of 8-oxo-dG in the lung DNA was assessed using a reverse phase HPLC system coupled with UV and electrochemical (EC) detection. After 13 weeks of exposure, measurements were made on lung samples obtained at the end of the exposure and a 44-week recovery period in clean air. Lung burdens of CB were determined at both time points as well as differential cell populations from bronchoalveolar lavage fluid (BAL). The results indicate that lung particle overload was achieved after exposure to 7 and 50 mg/m(3) (Printex-90) and 50 mg/m3 (Sterling V) but not at 1 mg/m(3) (Printex-90). Consistent with these results, a significant increase (P < 0.05) in 8-oxo-dG induction was observed following 13 weeks of exposure to 50 mg/m(3) Printex-90 and at 7 and 50 mg/m(3) after the 44-week recovery period. Interestingly, no increase in 8-oxo-dG was observed for Sterling V CB at either time point despite lung particle overload. Although the retained mass dose of Sterling V at the end of exposure was even higher than for Printex 90 (50 mg/m(3) exposure group) (approximately 7.6 vs 4.8 mg), the surface area of the retained Sterling V was similar to that of the retained Printex 90 of the mid-dose exposure (7 mg/m(3)) (approximately 0.2 m(2) in both groups). Since both Sterling V (50 mg/m(3)) and Printex 90 (7 mg/m(3)) did not induce significant increases in 8-oxo-dG in the lung at the end of the 13-week exposure, this finding indicates that a retained large particle mass is not always correlated with similar adverse effects but that particle surface area is a better dose parameter. The lower effect per unit mass dose seen with Sterling V is consistent with earlier studies showing that particle surface area of low toxicity particles is a more appropriate dosemetric for induction of inflammation in the lungs than particle mass (Oberdörster et al., 1994, 2001; Brown et al. 2001; Donaldson et al., 2002). An increase (p < 0.05) in lung lavage neutrophils was observed at 7 mg/m(3) (Printex-90) and 50 mg/m(3) (Printex-90 and Sterling V) at the 13-week exposure period and again at 50 mg/m(3) (Printex-90 and Sterling V, 44-week recovery period). Our current findings suggest that prolonged, high-dose exposure to CB can promote oxidative DNA damage that is consistent with the hypothesis that inflammatory cell-derived oxidants may play a role in the pathogenesis of rat lung tumors following long-term high-dose exposure to CB in rats.

Oxidative DNA damage in vitamin C-supplemented guinea pigs after intratracheal instillation of diesel exhaust particles

The health effects of diesel exhaust particles (DEP) are thought to involve oxidative damage. We have investigated the effect of intratracheal DEP instillation to guinea pigs in three groups of 12 animals each given 0, 0.7, or 2.1 mg. Five days later guinea pigs exposed to DEP had increased levels of oxidized amino acids (gamma-glutamyl semialdehyde), DNA strand breaks, and 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) in the lung. Bulky DNA ad- ducts were not significantly elevated in the lung. The antioxidant enzyme activity of glutathione reductase was increased in the lung of DEP-exposed guinea pigs, whereas glutathione peroxidase and superoxide dismutase enzyme activities were unaltered. There was no difference in DNA strand breaks in lymphocytes or urinary excretion of 8-oxodG at the two doses tested. Protein oxidations in plasma and in erythrocytes were not altered by DEP exposure. The concentrations of ascorbate in liver, lung, and plasma were unaltered by the DEP exposure. The results indicate that in guinea pigs DEP causes oxidative DNA damage rather than bulky DNA adducts in the lung. Guinea pigs, which are similar to humans with respect to vitamin C metabolism, may serve as a new model for the study of oxidative damage induced by particulate matter.

Oxidative-stress potency of organic extracts of diesel exhaust and urban fine particles in rat heart microvessel endothelial cells

Exposure to fine particulate materials is associated with an increase in mortality rate of cardiovascular diseases. Particles deposited in the lung may affect the vascular system both directly (leaching of soluble components from particles) and indirectly (via cytokines and mediators). The present study addressed cytotoxicity and oxidative stress potency of organic extracts of diesel exhaust particles (OE-DEP) and urban fine particles (OE-UFP) in rat heart microvessel endothelial (RHMVE) cells. The LC(50) values of OE-DEP and OE-UFP were calculated to be 17 and 34 microg/ml, respectively, suggesting that OE-DEP was more cytotoxic than OE-UFP. The viability of OE-DEP- and OE-UFP-exposed cells was ameliorated by N-acetyl-L-cysteine (NAC). The cell monolayer was exposed to 0 (control), 1, 3, and 10 microg/ml OE-DEP for 6 h and mRNA levels of antioxidant enzymes such as heme oxygenase-1 (HO-1), thioredoxin peroxidase 2 (TRPO), glutathione S-transferase P subunit (GST-P), and NADPH dehydrogenase (NADPHD) were quantitated by northern analysis. All those mRNA levels increased dose-dependently with OE-DEP and HO-1 mRNA showed the most marked response to OE-DEP. mRNA levels of those antioxidant enzymes and heat shock protein 72 (HSP72) in OE-DEP-exposed cells were higher than those of OE-UFP-exposed cells as compared at the same concentration. The transcription levels of HO-1 and HSP72 in OE-DEP- and OE-UFP-exposed cells were also reduced by NAC. Those results suggest that the organic fraction of particulate materials in the urban air has a potency to cause oxidative stress to endothelial cells and may be implicated in cardiovascular diseases through functional changes of endothelial cells.

Diesel exhaust particle-induced cell death of cultured normal human bronchial epithelial cells

We investigated the effect of diesel exhaust particles (DEPs) on normal human bronchial epithelial (NHBE) cells. Inclusion of DEPs in culture media was lethal to NHBE cells. NHBE cells are more susceptible to DEPs than other normal human lung cells, normal human pulmonary artery endothelial cells and normal human embryonic lung fibroblasts. DEP-induced cell death was mainly due to necrosis. Using the fluorescence probes diacetoxymethyl 6-carboxy-3',6'-diacetoxy-2',7'-dichloro-3',6'-dideoxydihydrofluorescinate and 4,5-diaminofluorescein diacetate, it was observed that hydrogen peroxide and nitrogen monoxide, respectively, were generated within DEP-exposed NHBE cells. DEP cytotoxicity increased or decreased with an increase or decrease in the cellular level of reduced glutathione (GSH) by treatment with L-buthionine-(R,S)-sulfoximine or ethyl reduced glutathionate, respectively. In addition, DEPs themselves decreased the cellular level of GSH in a dose-dependent manner. Upon exposure of NHBE cells to high concentrations of DEPs, their cellular GSH was depleted almost throughout. Further, the following agents decreased DEP cytotoxicity: 1) antioxidants 2,2,5,7,8-pentamethylchroman-6-ol, ebselen, and N,N'-bis(salicylidene)ethylenediaminomanganese(II) dihydrate (EUK-8); 2) iron ion-chelating agents disodium bathophenanthrolinedisulfonate and desferrioxamine mesylate; 3) nitrogen monoxide synthase inhibitors N(G)-nitro-L-arginine methyl ester hydrochloride and N(G)-methyl-L-arginine acetate salt; and 4) an endocytosis inhibitor quinacrine. On the basis of these observations, the mechanism of DEP cytotoxicity toward NHBE cells is discussed.

Isolation of nitrophenols from diesel exhaust particles (DEP) as vasodilatation compounds

The compounds in diesel exhaust particles (DEP) that are responsible for vasodilatation were isolated and characterized for the first time. From benzene extract of DEP, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenl and 4-nitrophenol were isolated, and their vasodilatation activities were confirmed. 3-methyl-4-nitrophenol caused dilatation of rat thoracic artery, and the other two nitrophenols, also showed vasodilatation activities.

A dimeric mechanism for contextual target recognition by MutY glycosylase

MutY, an adenine glycosylase, initiates the critical repair of an adenine:8-oxo-guanine base pair in DNA arising from polymerase error at the oxidatively damaged guanine. Here we demonstrate for the first time, using presteady-state active site titrations, that MutY assembles into a dimer upon binding substrate DNA and that the dimer is the functionally active form of the enzyme. Additionally, we observed allosteric inhibition of glycosylase activity in the dimer by the concurrent binding of two lesion mispairs. Active site titration results were independently verified by gel mobility shift assays and quantitative DNA footprint titrations. A model is proposed for the potential functional role of the observed polysteric and allosteric regulation in recruiting and coordinating interactions with the methyl-directed mismatch repair system.

Lower serum levels of beta-carotene in Lithuanian men are accompanied by higher urinary excretion of the oxidative DNA adduct, 8-hydroxydeoxyguanosine. The LiVicordia study

OBJECTIVE

In 1995, middle-aged Lithuanian men had a four-fold higher risk than Swedish men of dying from coronary heart disease. The cross-sectional LiVicordia study had reported significantly lower levels of the lipid-soluble antioxidants lycopene, beta-carotene, and gamma-tocopherol among Lithuanian men than among Swedish men. We examined whether there were differences in urinary 8-hydroxydeoxyguanosine (8OHdG), a marker of oxidative stress, between these groups of men.

METHODS

Using automated coupled column high-performance liquid chromatography with electrochemical detection, we examined 50-y-old men randomly sampled from Linköping, Sweden (n = 99) and Vilnius, Lithuania (n = 109) with regard to urinary concentrations of 8-OHdG.

RESULTS

Levels of 8-OHdG were higher in the Lithuanian men than in the Swedish men (20.9 +/- 0.91 versus 14.9 +/- 0.75 nM/L, P < 0.001), and this difference was evident in smokers (P < 0.01) and non-smokers (P < 0.001). Serum levels of alpha- and beta-carotene were inversely correlated to urinary 8-OHdG levels (P < 0.05 in both cases). Habitual smoking and low levels of beta-carotene contributed significantly to higher oxidative DNA damage expressed as urinary 8-OHdG.

CONCLUSIONS

These findings indicate that increased urinary 8-OHdG levels accompany lower serum levels of antioxidants in Lithuanian men. They supported previous suggestions that increased oxidative stress may be one factor behind the higher mortality in Lithuanian men.

Differential regulation of expression of hepatic and pulmonary cytochrome P4501A enzymes by 3-methylcholanthrene in mice lacking the CYP1A2 gene

The cytochrome P4501A enzymes play important roles in carcinogen metabolism. We reported previously that 3-methylcholanthrene (MC) elicits a persistent induction of hepatic, pulmonary, and mammary microsomal cytochrome P450 (P450) 1A enzymes for several weeks after MC withdrawal. In this study, we tested the hypothesis that CYP1A2, a liver-specific P450 isozyme, plays an important role in the mechanisms governing persistent CYP1A1 induction by MC in liver but not in extra-hepatic tissues such as lung, which is devoid of endogenous CYP1A2. Administration of wild-type (WT) or CYP1A2-null mice with MC (100 micromol/kg i.p.) once daily for 4 days caused significant increases in hepatic CYP1A1/1A2 activities, apoprotein contents, and mRNA levels 1 day after carcinogen withdrawal compared with vehicle-treated controls. The induction persisted in the WT, but not CYP1A2-null animals, for up to 15 days. In the lung, MC caused persistent CYP1A1 induction for 15 days in both the genotypes. Since MC is almost completely eliminated by day 15, we hypothesize that CYP1A2 contributes to the up-regulation of CYP1A1 in liver, but not lung, by a novel mechanism, presumably involving a CYP1A2-dependent persistent metabolite. The studies demonstrate tissue-specific differences in the regulation of CYP1A by MC, a phenomenon that may have implications for human carcinogenesis caused by environmental chemicals.

The dual effect of the particulate and organic components of diesel exhaust particles on the alteration of pulmonary immune/inflammatory responses and metabolic enzymes

Exposure to diesel exhaust particles (DEP) is an environmental and occupational health concern. This review examines the cellular actions of the organic and the particulate components of DEP in the development of various lung diseases. Both the organic and the particulate components cause oxidant lung injury. The particulate component is known to induce alveolar epithelial damage, alter thiol levels in alveolar macrophages (AM) and lymphocytes, and activate AM in the production of reactive oxygen species (ROS) and pro-inflammatory cytokines. The organic component, on the other hand, is shown to generate intracellular ROS, leading to a variety of cellular responses including apoptosis. There are a number of differences between the biological actions exerted by these two components. The organic component is responsible for DEP induction of cytochrome P450 family 1 enzymes that are critical to the polycyclic aromatic hydrocarbons (PAH) and nitro-PAH metabolism in the lung as well as in the liver. The particulate component, on the other hand, causes a sustained down-regulation of CYP2B1 in the rat lung. The significance of this effect on pulmonary metabolism of xenobiotics and endobiotics remains to be seen, but may prove to be an important factor governing the interplay of the pulmonary metabolic and inflammatory systems. Long-term exposures to various particles including DEP, carbon black (CB), TiO2, and washed DEP devoid of the organic content, have been shown to produce similar tumorigenic responses in rodents. There is a lack of correlation between tumor development and DEP chemical-derived DNA adduct formation. But the organic component has been shown to generate ROS that produce 8-hydroxydeoxyguanosine (8-OHdG) in cell culture. The organic, but not the particulate, component of DEP suppresses the production of pro-inflammatory cytokines by AM and the development of Th1 cell-mediated immunity. The mechanism for this effect is not yet clear, but may involve the induction of heme oxygenase-1 (HO-1), a cellular genetic response to oxidative stress. Both the organic and the particulate components of DEP enhance respiratory allergic sensitization. Part of the DEP effects may be due to a depletion of glutathione in lymphocytes. The organic component, which is shown to induce IL-4 and IL-10 productions, may skew the immunity toward Th2 response, whereas the particulate component may stimulate both the Th1 and Th2 responses. In conclusion, the literature shows that the particulate and organic components of DEP exhibit different biological actions but both involve the induction of cellular oxidative stress. Together, these effects inhibit cell-mediated immunity toward infectious agents, exacerbate respiratory allergy, cause DNA damage, and under long-term exposure, induce the development of lung tumors.

Effect of diet on cancer development: is oxidative DNA damage a biomarker?

Free radicals and other reactive species are generated in vivo and many of them can cause oxidative damage to DNA. Although there are methodological uncertainties about accurate quantitation of oxidative DNA damage, the levels of such damage that escape immediate repair and persist in DNA appear to be in the range that could contribute significantly to mutation rates in vivo. The observation that diets rich in fruits and vegetables can decrease both oxidative DNA damage and cancer incidence is consistent with this. By contrast, agents increasing oxidative DNA damage usually increase risk of cancer development. Such agents include cigarette smoke, several other carcinogens, and chronic inflammation. Rheumatoid arthritis and diabetes are accompanied by increased oxidative DNA damage but the pattern of increased cancer risk seems unusual. Other uncertainties are the location of oxidative DNA damage within the genome and the variation in rate and level of oxidative damage between different body tissues. In well-nourished human volunteers, fruits and vegetables have been shown to decrease oxidative DNA damage in several studies, but data from short-term human intervention studies suggest that the protective agents are not vitamin C, vitamin E, beta-carotene, or flavonoids.

Human 8-oxoguanine DNA glycosylase 1 mRNA expression as an oxidative stress exposure biomarker of cooking oil fumes

Epidemiological studies have indicated that the exposure to carcinogenic components formed during the cooking of food might be associated with lung cancer risk of Chinese women. Previous studies have confirmed that cooking oil fumes from frying fish (COF) contained relatively high amount of benzo[a]pyrene, 2-methyl-3,8-dimethylimidazo[4,5-f] qunoxaline, benzene, and 1,3-butadiene, reported in fumes from heated soybean oil. Thus, we consider that oxidative stress induced by COF may play a role in lung cancer development among Chinese women. To verify whether the oxidative DNA damage was induced by COF, high-performance liquid chromatography (HPLC) analysis data showed that the levels of 8-hydroxydeoxyguanine (8-OH dG) were increased in a dose-dependent manner when calf thymus DNA reacted with various concentrations of COF. Since human 8-oxoguanine DNA glycosylase 1 (hOGG1) was a repair enzyme for removing 8- OH dG from damaged DNA, we hypothesized that hOGG1 mRNA may be used to assess the risk of oxidative damage induced by the exposure of COF. The results from reverse-transcription polymerase chain reaction showed that the hOGG1 mRNA expression was induced by hydrogen peroxide (H2O2) and COF in human lung adenocarcinoma CL-3 cells. To elucidate whether hOGG1 mRNA expression was an exposure biomarker of COF, a cross-sectional study of 238 subjects including 94 professional cooks, 43 housewives, and 101 COF-nonexposed control subjects was conducted. The hOGG1 mRNA expression frequencies of COF-exposed cooks (27 of 94, 28.7%) and housewives (6 of 43, 14%) were significantly higher than those of control subjects (4 of 101, 4%). After adjusting for age, sex, and smoking and drinking status, the odds risks (ORs) of housewives versus control and cooks versus control were 3.94 (95% confidence interval [CI] = 0.95-16.62) and 10.12 (95% CI = 2.83-36.15), respectively. These results indicated that hOGG1 may be adequate to act as an exposure biomarker to assess the oxidative DNA damage induced by COF. This also suggests that oxidative stress induced by COF may play a role in lung cancer development among Chinese women.

Oxidative DNA damage in prostate cancer patients consuming tomato sauce-based entrees as a whole-food intervention

BACKGROUND

Human prostate tissues are vulnerable to oxidative DNA damage. The risk of prostate cancer is lower in men reporting higher consumption of tomato products, which contain high levels of the antioxidant lycopene. We examined the effects of consumption of tomato sauce-based pasta dishes on lycopene uptake, oxidative DNA damage, and prostate-specific antigen (PSA) levels in patients already diagnosed with prostate cancer.

METHODS

Thirty-two patients with localized prostate adenocarcinoma consumed tomato sauce-based pasta dishes for the 3 weeks (30 mg of lycopene per day) preceding their scheduled radical prostatectomy. Serum and prostate lycopene concentrations, serum PSA levels, and leukocyte DNA oxidative damage (ratio of 8-hydroxy-2'-deoxyguanosine [8-OHdG] to 2'-deoxyguanosine [dG]) were assessed before and after the dietary intervention. DNA oxidative damage was assessed in resected prostate tissue from study participants and from seven randomly selected prostate cancer patients. All statistical tests were two-sided.

RESULTS

After the dietary intervention, serum and prostate lycopene concentrations were statistically significantly increased, from 638 nM (95% confidence interval [CI] = 512 to 764 nM) to 1258 nM (95% CI = 1061 to 1455 nM) (P<.001) and from 0.28 nmol/g (95% CI = 0.18 to 0.37 nmol/g) to 0.82 nmol/g (95% CI = 0.57 to 1.11 nmol/g) (P <.001), respectively. Compared with preintervention levels, leukocyte oxidative DNA damage was statistically significantly reduced after the intervention, from 0.61 8-OHdG/10(5) dG (95% CI = 0.45 to 0.77 8-OHdG/10(5) dG) to 0.48 8-OHdG/ 10(5) dG (95% CI = 0.41 to 0.56 8-OHdG/10(5) dG) (P =.005). Furthermore, prostate tissue oxidative DNA damage was also statistically significantly lower in men who had the intervention (0.76 8-OHdG/10(5) dG [95% CI = 0.55 to 0.96 8-OHdG/10(5) dG]) than in the randomly selected patients (1.06 8-OHdG/10(5) dG [95% CI = 0.62 to 1.51 8-OHdG/10(5) dG]; P =.03). Serum PSA levels decreased after the intervention, from 10.9 ng/mL (95% CI = 8.7 to 13.2 ng/mL) to 8.7 ng/mL (95% CI = 6.8 to 10.6 ng/mL) (P<.001).

CONCLUSION

These data indicate a possible role for a tomato sauce constituent, possibly lycopene, in the treatment of prostate cancer and warrant further testing with a larger sample of patients, including a control group.

The role of oxidative stress in indium phosphide-induced lung carcinogenesis in rats

Indium phosphide (IP), widely used in the microelectronics industry, was tested for potential carcinogenicity. Sixty male and 60 female Fischer 344 rats were exposed by aerosol for 6 h/day, 5 days/week, for 21 weeks (0.1 or 0.3 mg/m(3); stop exposure groups) or 105 weeks (0 or 0.03 mg/m(3) groups) with interim groups (10 animals/group/sex) evaluated at 3 months. After 3-month exposure, severe pulmonary inflammation with numerous infiltrating macrophages and alveolar proteinosis appeared. After 2 years, dose-dependent high incidences of alveolar/bronchiolar adenomas and carcinomas occurred in both sexes; four cases of squamous cell carcinomas appeared in males (0.3 mg/m(3)), and a variety of non-neoplastic lung lesions, including simple and atypical hyperplasia, chronic active inflammation, and squamous cyst, occurred in both sexes. To investigate whether inflammation-related oxidative stress functioned in the pathogenesis of IP-related pulmonary lesions, we stained lungs of control and high-dose animals immunohistochemically for four markers indicative of oxidative stress: inducible nitric oxide synthase (i-NOS), cyclooxygenase-2 (COX-2), glutathione-S-transferase Pi (GST-Pi), and 8-hydroxydeoxyguanosine (8-OHdG). Paraffin-embedded samples from the 3-month and 2-year control and treated females were used. i-NOS and COX-2 were highly expressed in inflammatory foci after 3 months; at 2 years, all four markers were expressed in non-neoplastic and neoplastic lesions. Most i-NOS staining, mainly in macrophages, occurred in chronic inflammatory and atypical hyperplastic lesions. GST-Pi and 8-OHdG expression occurred in cells of carcinoma epithelium, atypical hyperplasia, and squamous cysts. These findings suggest that IP inhalation causes pulmonary inflammation associated with oxidative stress, resulting in progression to atypical hyperplasia and neoplasia.

Strain variation in renal carcinogenesis by N-ethyl-N-hydroxyethylnitrosamine in F1 (Wistar-Fischer) rats

The present study was conducted to compare the incidences of renal tumors in Wistar (W), Fischer (F) and F1 rats (WF: female Wistar rats x male Fischer rats; FW: female Fischer rats x male Wistar rats) induced by N-ethyl-N-hydroxyethylnitrosamine (EHEN). Levels of 8-OHdG in renal DNA were also investigated in Wistar and Fischer rats. After 2000 ppm of EHEN was administered orally for 2 weeks, the animals were fed basal diet until week 32. Wistar males and females demonstrated significantly higher sensitivity regarding induction of renal lesions, while both WF and FW rats had similar incidences, generally intermediate between those for the two parent strains. The formation of 8-OHdG was maximal 60-180 min after an intraperitoneal dose of 750 mg/kg to Wistar and Fischer rats, which correlates with the increase tending to the incidence of renal tumors in male and female Wistar and Fischer rats. The results suggest that EHEN induction of renal tumors is related to oxygen radical damage and that the genes in the Wistar strain responsible for the sensitivity are not inherited in a sex-dependent fashion, despite the male being more susceptible.

Accelerated DNA adduct formation in the lung of the Nrf2 knockout mouse exposed to diesel exhaust

Diesel exhaust (DE) has been recognized as a noxious mutagen and/or carcinogen, because its components can form DNA adducts. Mechanisms governing the susceptibility to DE and the efficiency of such DNA adduct formation require clarification. The transcription factor Nrf2 is essential for inducible and/or constitutive expression of a group of detoxification and antioxidant enzymes, and we hypothesized that the nrf2 gene knockout mouse might serve as an excellent model system for analyzing DE toxicity. To address this hypothesis, lungs from nrf2(-/-) and nrf2(+/-) mice were examined for the production of xenobiotic-DNA adducts after exposure to DE (3 mg/m(3) suspended particulate matter) for 4 weeks. Whereas the relative adduct levels (RAL) were significantly increased in the lungs of both nrf2(+/-) and nrf2(-/-) mice upon exposure to DE, the increase of RAL in the lungs from nrf2(-/-) mice exposed to DE were approximately 2.3-fold higher than that of nrf2(+/-) mice exposed to DE. In contrast, cytochrome P4501A1 mRNA levels in the nrf2(-/-) mouse lungs were similar to those in the nrf2(+/-) mouse lungs even after exposure to DE, suggesting that suppressed activity of phase II drug-metabolizing enzymes is important in giving rise to the increased level of DNA adducts in the Nrf2-null mutant mouse subjected to DE. Importantly, severe hyperplasia and accumulation of the oxidative DNA adduct 8-hydroxydeoxyguanosine were observed in the bronchial epidermis of nrf2(-/-) mice following DE exposure. These results demonstrate the increased susceptibility of the nrf2 germ line mutant mouse to DE exposure and indicate the nrf2 gene knockout mouse may represent a valuable model for the assessment of respiratory DE toxicity.

Benzo(a)pyrene-coated onto Fe(2)O(3) particles-induced lung tissue injury: role of free radicals

Lipid peroxidation (as malondialdehyde; MDA), activities of some antioxidant enzymes (as superoxide dismutase; SOD, glutathione peroxidase; GPx, glutathione reductase; GR), glutathione status, and oxidative DNA damage (as 8-hydroxy-2'-deoxyguanosine; 8-OHdG) were investigated in the lungs of rats exposed to hematite (Fe(2)O(3); 3 mg), benzo(a)pyrene (B(a)P; 3 mg), or B(a)P (3 mg)-coated onto Fe(2)O(3) particles (3 mg). Approximately 2-fold increases in MDA production were seen in animals exposed to Fe(2)O(3), B(a)P, or B(a)P-coated onto Fe(2)O(3) particles (P<0.01). Decreases in SOD activities were observed in rats treated with Fe(2)O(3) (1.66-fold, P<0.01), B(a)P (1.66-fold, P<0.001) or B(a)P-coated onto Fe(2)O(3) particles (1.43-fold, P<0.01). GPx and GR activities could not be detected. No alteration of the glutathione status was observed. Significant increases in the 8-OHdG formation occurred in response to exposure to B(a)P (2.0-fold, P<0.01) or B(a)P-coated onto Fe(2)O(3) particles (23.7-fold, P<0.001). Our results demonstrate also that Fe(2)O(3) generates free radical (FR)-induced lung injury and is not an inert carrier. We established that exposure to B(a)P or B(a)P-coated onto Fe(2)O(3) particles resulted in lipid peroxidation and SOD inactivation, thereby leading to oxidative damages in DNA. The main findings of this work was that B(a)P-coated onto Fe(2)O(3) particles caused higher lung concentrations of 8-OHdG than B(a)P by itself. Hence, our data may explain why exposure to B(a)P-coated onto Fe(2)O(3) particles resulted in a decreased latency and an increased incidence of lung tumors in rodents compared to exposure to B(a)P.

Mechanism of oxidative DNA damage induced by carcinogenic 4-aminobiphenyl

DNA adduct formation is thought to be a major cause of DNA damage by carcinogenic aromatic amines. We investigated the ability of an aromatic amine, 4-aminobiphenyl (4-ABP) and its N-hydroxy metabolite (4-ABP(NHOH)) to cause oxidative DNA damage, using (32)P-labeled human DNA fragments from the p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. 4-ABP(NHOH) was found to cause Cu(II)-mediated DNA damage, especially at thymine residues. Addition of the endogenous reductant NADH led to dramatic enhancement of this process. Catalase and bathocuproine, a Cu(I)-specific chelator, reduced the amount of DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). 4-ABP(NHOH) dose-dependently induced 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in the presence of Cu(ll) and NADH. 4-ABP(NHOH) conversion to nitrosobiphenyl, as measured by UV-visible spectroscopy, occurred rapidly in the presence of Cu(II), suggesting Cu(II)-mediated autoxidation. Increased amounts of 8-OHdG were found in HL-60 cells compared to the H(2)O(2)-resistant clone HP100 following 4-ABP(NHOH) treatment, further supporting the involvement of H(2)O(2). The present study demonstrates that an N-hydroxy derivative of 4-ABP induces oxidative DNA damage through H(2)O(2) in both a cell-free system and in cultured human cells. We conclude that, in addition to DNA adduct formation, oxidative DNA damage may play an important role in the carcinogenic process of 4-ABP.

Diesel exhaust particle-induced cell death of human leukemic promyelocytic cells HL-60 and their variant cells HL-NR6

The cytotoxicity of diesel exhaust particles (DEPs) toward human leukemic promyelocytic cells HL-60 was examined. DEPs were toxic and cytotoxicity increased in a dose-dependent manner. All cells died with 750 microg/ml DEPs in culture media. Apoptosis occurred in HL-60 cells exposed to DEPs. The cytotoxicity of DEP extracts with organic solvents was much lower than those of DEPs and organic solvent-washed residual DEPs. HL-NR6 cells, an HL-60 variant cell line, having higher superoxide dismutase and catalase activities than HL-60 cells, were more resistant to DEP cytotoxicity. When preincubated with the fluorescent probe diacetoxymethyl 6-carboxy-2',7'-dichlorodihydrofluorescinate diacetate and then exposed to DEPs, HL-60 cells emitted green fluorescence under blue illumination, indicating that reactive oxygen species were generated within the cells. The DEP cytotoxicity correlated inversely with the cellular concentration of reduced glutathione (GSH), which had been attenuated with L-buthionine-(R,S)-sulfoximine, a gamma-glutamylcysteine synthetase inhibitor, and was lowered with ethyl reduced glutathionate, a GSH carrier across biomembranes. Further, DEPs themselves decreased the cellular concentration of GSH in a dose-dependent manner. The alpha-tocopherol model compound 2,2,5,7,8-pentamethylchroman-6-ol decreased DEP cytotoxicity, while alpha-tocopherol had no effect. In addition, quinacrine, an endocytosis inhibitor, decreased DEP cytotoxicity. These results show that DEPs are cytotoxic and suggest that the cytotoxicity results from generation of reactive oxygen species by DEPs which have been incorporated into cells.

Inhibition of 1,2-dimethylhydrazine-induced oxidative DNA damage in rat colon mucosa by black tea complex polyphenols

The effect of black tea polyphenols on 1,2-dimethylhydrazine (DMH)-induced oxidative DNA damage in rat colon mucosa has been investigated. Fischer 344 rats were treated orally with thearubigin (TR) or theafulvin (TFu) for 10 days (40 mg/kg), injected ip with DMH (20 mg/kg) or saline and sacrificed 24 hr after DMH administration. The levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured in colonic mucosa DNA and expressed as a ratio relative to 2'-deoxyguanosine (2dG). Control rat mucosa had 8-OHdG values of 1.12 +/- 0.14/10(5) dG (mean +/- SEM, n=11), whereas DMH-treated rats significantly higher values (1.52 +/- 0.14/10(5) dG, n=26, P<0.05). Pretreatment of rats with TR had significantly inhibited DMH-induced oxidative DNA damage 0.99 +/- 0.09/10(5) dG, n=10, P<0.05) and a similar, although less marked, effect was observed with TFu (1.15 +/- 0.19/10(5), n=9, P=0.06). These findings confirm that DMH causes oxidative DNA damage in the colon mucosa of rats and demonstrate that this effect is prevented by the consumption of complex polyphenols from black tea.

Early oxidative DNA damages and late development of lung cancer in diesel exhaust-exposed rats

To demonstrate DNA damages in the early stage of diesel exhaust exposure, an inhalation study of 1 through 12 months was conducted. The lung burden of diesel soot increased with increase in exposure duration. Histologically, hyperplastic foci of alveolar epithelia were found at 6-month exposure and became prominent at the 12th month, with slight nuclear atypia and positive p53 staining. The level of 8-OH-hydroxyguanosine (8-OH-dG) in the exposed rat lungs showed an increase from 1 month of exposure, followed by a gradual increase, reaching almost a plateau level at the 9th month. An in vitro experiment demonstrated significant 8-OH-dG formation when diesel particles and H(2)O(2) were added to the DNA solution. The level of bulky aromatic DNA adducts peaked at the 1st month of exposure, followed by a decrease. By the end of the observation period of 30 months, lung tumors developed even in the 6-month exposure group, and the earliest lung tumors were found only in rats that survived longer than 18 months. In conclusion, persisting oxidative stress on DNA induced in the early phase of diesel exhaust exposure, together with inflammation, seems to play an important role in carcinogenesis at advance ages after a long latent period.

Increase in mutation frequency in lung of Big Blue rat by exposure to diesel exhaust

Exposure to diesel exhaust (DE) is known to cause lung tumors in rats. To clarify the mutagenicity of DE, we estimated mutant frequency (MF) and determined the mutation spectra in rat lung after exposure to DE using lambda/lacI transgenic rats (Big Blue system). Male Big Blue rats (6 weeks old) were exposed for 4 weeks to 1 or 6 mg/m(3) DE, which contains suspended particulate matter. Control rats were maintained in filtered clean air. After exposure to 6 mg/m(3) DE, MF in lung was 4.8-fold higher than in control rats (P < 0.01), but no increase in MF was observed in rats exposed to 1 mg/m(3) DE. Sixty-nine mutants were identified after exposure to 6 mg/m(3) DE. The major mutations were A:T-->G:C (18 mutations) and G:C-->A:T (19 mutations) transitions. Remarkably, G-->T transversion of the lacI gene at site 221 was a hot-spot induced by exposure to DE, and there were complex mutations in which multiple mutations occurred in a single mutant, especially in the rats exposed to 6 mg/m(3) DE. DNA adducts formed by DE were analyzed using a (32)P-post-label TLC method and the amount of 8-hydroxydeoxyguanosine (8-OHdG) was measured using HPLC. Relative adduct level and amount of 8-OHdG were significantly increased in the rats exposed to 6 mg/m(3) DE compared with the controls (3.0- and 2.2-fold, respectively; P < 0.01). The level of cytochrome P450 1A1 mRNA was shown by northern blot analysis to be significantly increased in the lungs of rats exposed to 6 mg/m(3) DE (5.5-fold; P < 0.01). These results indicate that DE causes lesions in genomic DNA and acts as a mutagen in rat lung.

Levels of 8-hydroxydeoxyguanosine as a marker of DNA damage in human leukocytes

We measured 8-hydroxy-2-deoxyguanosine (8-OHdG) levels in human leukocytes from healthy donors to evaluate oxidative DNA damage and its correlation with smoking, physical exercise, and alcohol consumption. A significant increase in oxidative DNA damage was induced by cigarette smoke, with the mean level of 8-OHdG being significantly higher in smokers (33.1 +/- 10.6 per 10(6) 2-deoxyguanosine (dG) [mean +/- SE], n = 16) compared with nonsmokers (15.3 +/- 1.8 per 10(6) dG, n = 31) and former smokers (17.8 +/- 1.5 per 10(6) dG, n = 9). The highest values were observed after smoking more than 10 cigarettes per day (41.8 +/- 17.1 per 10(6) dG, n = 9). A large interindividual variation in 8-OHdG levels was observed in all analyzed groups. We also observed a correlation between 8-OHdG levels and age in nonsmokers and former smokers. Neither frequency of physical exercise nor alcohol drinking significantly modified 8-OHdG levels in leukocytes.

8-Hydroxyguanosine formed in human lung tissues and the association with diesel exhaust particles

Diesel exhaust particles consist of various organic chemicals, heavy metals, and carbon particles. Knowledge of the fate of organic chemicals and carbon particles in the lungs is important to determine the mechanisms responsible for lung tumors. In the present study, diesel particle extracts were found to show mutagenicity for YG3003, a sensitive strain to some oxidative mutagens, as well as other mutant strains, and those of lung tissues obtained from lung cancer patients exhibited potent mutagenicity. Formation of 8-hydroxyguanosine (8-OHdG) as a biomarker of oxidative damage was analyzed with in vitro and in vivo assay systems. The 8-OHdG was detected in all 22 cases of lung tissues with carcinomas tested and their levels increased with the increasing age of the patients, suggesting a correlation between age and the presence of carbon particles in lung tissues. Therefore, the formation of 8-OHdG due to diesel exhaust particles was investigated via intratracheal injections into mice. 8-OHdG formation was elevated when carboneceous particles, after removal of organic chemicals with various solvents, were administered to mice, but it was not elevated when polyaromatic compounds such as benzo[a]pyrene, 1,8-dinitropyrene, and 1-nitropyrene were used in the same procedure in mice. The carboneceous particles were formed from a giant particle that was aggregated by micro-particles with diameters of 1.47 +/- 1.34 to 1.05 +/- 0.83 microm. These results suggest that carboneceous particles, but not mutagens and carcinogens, promote the formation of 8-OHdG, and that as a mechanism, alveolar macrophages may be involved in oxidative damage. The oxidative damage may be due to the fact that the mutation is involved with the generation of a hydroxyl radical during phagocytosis, and the hydroxyl radical leads to hydroxylation at the C-8 position of the deoxyguanosine residue in the DNA.

Chemicals in Diesel Exhaust Particles Generate Reactive Oxygen Radicals and Induce Apoptosis in Macrophages

There is increasing evidence that particulate air pollutants, such as diesel exhaust particles (DEP), potentiate chronic inflammatory processes as well as acute symptomatic responses in the respiratory tract. The mechanisms of action as well as the cellular targets for DEP remain to be elucidated. We show in this paper that the phagocytosis of DEP by primary alveolar macrophages or macrophage cell lines, RAW 264.7 and THP-1, leads to the induction of apoptosis through generation of reactive oxygen radicals (ROR). This oxidative stress initiates two caspase cascades and a series of cellular events, including loss of surface membrane asymmetry and DNA damage. The apoptotic effect on macrophages is cell specific, because DEP did not induce similar effects in nonphagocytic cells. DEP that had their organic constituents extracted were no longer able to induce apoptosis or generate ROR. The organic extracts were, however, able to induce apoptosis. DEP chemicals also induced the activation of stress-activated protein kinases, which play a role in cellular apoptotic pathways. The injurious effects of native particles or DEP extracts on macrophages could be reversed by the antioxidant, N-acetyl-cysteine. Taken together, these data suggest that organic compounds contained in DEP may exert acute toxic effects via the generation of ROR in macrophages.

Tumorigenic conversion of a rat urothelial cell line by human polymorphonuclear leukocytes activated by lipopolysaccharide

Chronic inflammation is a significant risk factor for the development of urinary bladder cancer. We have shown that inflammation induced by killed Escherichia coli and also by its lipopolysaccharide (LPS) strikingly enhances N-methyl-N-nitrosourea (MNU)-initiated rat bladder carcinogenesis. Aspirates from the bladder lumen contained a large quantity of hydrogen peroxide (H2O2) and several cytokines. In this study, we tested the hypothesis that reactive oxygen intermediates (ROI) released from activated polymorphonuclear leukocytes (PMN) are involved in inflammation-associated bladder carcinogenesis. Using an immortalized nontumorigenic rat urothelial cell line, MYP3, we examined the effect of LPS-activated PMN on malignant transformation. MYP3 cells pretreated with or without MNU were exposed daily to LPS-activated PMN for one week and were then tested for growth in soft agar. In contrast to no colony formation by the parental cells, a varying number of colonies developed from cells treated with LPS-activated PMN. Although combined treatment with MNU and PMN was most effective (P<0.01), cells treated with LPS-activated PMN alone also formed a small number of colonies. Addition of catalase, which decomposes H2O2, and/or an antioxidant, alpha-tocopherol, reduced the number of colonies induced by LPS-activated PMN (P<0.05). Cells derived from colonies were tumorigenic in athymic nude mice. However, tumorigenicity in mice was greater with cells treated with both MNU and PMN than with cells treated with PMN alone. Our results suggest that ROI released from LPS-activated PMN may be one of the mechanisms involved in the carcinogenesis associated with active urinary tract infection.

PUVA (8-methoxy-psoralen plus ultraviolet A) induces the formation of 8-hydroxy-2'-deoxyguanosine and DNA fragmentation in calf thymus DNA and human epidermoid carcinoma cells

The objective of this study is to investigate if 8-methoxy-psoralen (8-MOP) plus ultraviolet A (UVA) radiation (PUVA) induces oxidative DNA damage. When calf thymus DNA was incubated with 8-MOP and irradiated with UVA (335-400 nm), the level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) was substantially increased by approximately 6-fold. Formation of 8-OHdG proportionally correlated with both UVA fluence and 8-MOP concentrations. Human epidermoid carcinoma cells were incubated with 10 microg 8-MOP per milliliter, followed by irradiation of 25 kJ/m2 UVA. The level of 8-OHdG increased by nearly 3-fold in PUVA-treated cells compared to 8-MOP and UVA controls. The formation of 8-OHdG correlated with DNA fragmentation as determined by spectrofluorometry. To investigate the reactive oxygen species (ROS) involved in PUVA-induced oxidative DNA damage, less or more specific ROS quenchers were added to DNA solution prior to PUVA treatment. The results showed that only sodium azide and genistein significantly quenched PUVA-induced 8-OHdG, whereas catalase, superoxide dismutase, and mannitol exhibited no effect. The quencher study with cultured cells indicated that N-acetyl-cysteine and genistein protected oxidative DNA damage as well as DNA fragmentation by PUVA treatment. Our studies show that PUVA treatment is able to induce the formation of 8-OHdG in purified DNA and cultured cells and suggest that singlet oxygen is the principle reactive oxygen species involved in oxidative DNA damage by PUVA treatment.

Generation of reactive oxygen species and 8-hydroxy-2'-deoxyguanosine formation from diesel exhaust particle components in L1210 cells

The generation of the reactive oxygen species during the interaction of diesel exhaust particles (DEP) with NADPH-cytochrome P450 reductase (P450 reductase) was investigated by electron spin resonance using the spin-trap 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Addition of DEP extract to an incubation mixture of mouse lung microsomes in the presence of NADPH resulted in a time-dependent NADPH oxidation and acetylated-cytochrome c reduction. Using purified P450 reductase as the enzyme source, superoxide radicals which were detected as the spin adduct (DMPO-OOH) while metabolized by P450 reductase were dependent upon both DEP and enzyme concentrations. The ELISA method using a specific monoclonal antibody revealed that DEP produced 8-hydroxy-2'-deoxyguanosine (8-OHdG), which is formed from deoxyguanosine in DNA by hydroxyl radicals, in the culture medium of L1210 cells. Active oxygen scavengers such as superoxide dismutase and catalase effectively blocked the formation of 8-OHdG in culture medium, and deferoxamine, which inhibits hydroxyl radicals production by chelating iron, was also effective in inhibiting the DEP-produced 8-OHdG formation. These results indicate that DEP components produce 8-OHdG through the hydroxyl radical formation via superoxide by redox cycling of P450 reductase.

Increased urinary excretion of 8-oxo-2'-deoxyguanosine, a biomarker of oxidative DNA damage, in urban bus drivers

Oxidative damage to DNA could be involved in the increased risk of cancer associated with exposure to polluted urban air, which contains a number of oxidants. CYP1A2 is induced by and metabolizes polyaromatic hydrocarbons (PAH) and aromatic amines and could modify effects of exposure to ambient air pollution. Similarly, DNA repair may be influenced by occupational and other exposures as well as modify the effect of DNA damaging agents. As part of a large investigation of the genotoxic burden to diesel exposed workers in transport sectors we studied oxidative DNA damage in 57 non-smoking bus drivers from the greater Copenhagen area. The drivers were studied on a workday and on a day off work. Comparisons were made between drivers from the central (n=30) and rural/suburban (n=27) areas of Copenhagen. The rate of oxidative DNA damage was estimated from 24 h urinary excretion of 8-oxo-2'-deoxyguanosine (8-oxodG), a repair product of the highly mutagenic oxidation of guanine in DNA or the cellular pool of GTP. CYP1A2 activity was estimated from the urinary excretion of metabolites of dietary caffeine. The DNA repair was estimated by unscheduled DNA synthesis (UDS) in mononuclear cells isolated on the workday. Repeated measures ANOVA and multifactorial ANCOVA with CYP1A2 activity, age and UDS as covariates were used for statistical evaluation. On the workday, the 8-oxodG excretion was 190+/-108 and 146+/-89 pmol/kg 24 h in the bus drivers from central and the suburban/rural areas Copenhagen, respectively (p<0.05). The 8-oxodG excretion was not significantly different between the workday and the day off. CYP1A2 activity was not affected by driving area but was correlated with the 8-oxodG excretion on the workday (r=0.53; p<0.05). UDS was not significantly affected by driving area or correlated with the 8-oxodG excretion. The increased excretion of 8-oxodG in bus drivers from central Copenhagen as compared with drivers from rural/suburban greater Copenhagen suggests that exposure to ambient air pollution causes oxidative damage to DNA. This effect may be modified by the activity of CYP1A2 or a coregulated enzyme.

Endogenous oxidative damage of mtDNA

Almost a decade ago, based on analytical measurements of the oxidative DNA adduct 8-oxo-deoxyguanosine (oxo8dG), it was reported that mitochondrial DNA suffers greater endogenous oxidative damage than nuclear DNA. The subsequent discovery that somatic deletions of mitochondrial DNA occur in humans, and that they do so to the greatest extent in metabolically active tissues, strengthened the hypothesis that mitochondrial DNA is particularly susceptible to endogenous oxidative attack. This hypothesis was (and is) appealing for a number of reasons. Nevertheless, solid direct support for the hypothesis is lacking. Since the initial measurements, attempts to repeat the observation of greater oxidation of mitochondrial DNA have resulted in a range of measurements that spans over four orders of magnitude. Moreover, this range includes values that are as low as published values for nuclear DNA. In the last 2 years or so, it has become apparent that the quantification of oxidative DNA adducts is prone to artifactual oxidation. We have reported that the analysis of small quantities of DNA may be particularly susceptible to such interference. Because yields of mitochondrial DNA are generally low, a systematic artifact associated with low quantities of DNA may have elevated the apparent level of adduct oxo8dG in mitochondrial DNA relative to nuclear DNA in some studies. Whatever the cause for the experimental variation, the huge disparity between published measurements of oxidative damage makes it impossible to conclude that mitochondrial DNA suffers greater oxidation than nuclear DNA. Despite the present confusion, however, there are reasons to hypothesize that this is indeed the case. We briefly describe methods being developed by a number of workers that are likely to surmount current obstacles and allow the hypothesis to be tested definitively.

Effect of environmental pollutants on the production of pro-inflammatory cytokines by normal human dermal keratinocytes

The effect of the environmental pollutants, diesel exhaust particles (DEP) and formaldehyde (FA), on the production of pro-inflammatory cytokines (interleukin (IL)-1alpha, IL-1beta, tumor necrosis factor (TNF)-alpha and IL-8) by normal human dermal keratinocytes (hKCs) was investigated. Normal hKCs were incubated with various concentrations of DEP (0.4, 0.8, 4, or 20 microg/ml) or FA (0.25, 0.5, 1, or 5 microg/ml), and cytokine production was then determined by enzyme-linked immunosorbent assay (ELISA). DEP (20 microg/ml) induced IL-1beta production without altering cell growth. The increased production of IL-1beta induced by this concentration of DEP was further enhanced by the presence of phorbol 12-myristate 13-acetate (PMA), although PMA alone did not affect the levels of IL-1beta. IL-8 production was also increased by DEP (0.4 and 0.8 microg/ml), which is consistent with the results that these concentrations of DEP increased the number of cells significantly after 72 h incubation. Although FA alone did not stimulate the production of IL-1beta or IL-8 by keratinocytes, FA (0.5 microg/ml and 5 microg/ml) significantly increased IL-8 and IL-1beta production, respectively, in cells stimulated with PMA. IL-1alpha production was not modulated by FA or DEP even in the presence of PMA. TNF-alpha was produced by unstimulated keratinocytes at barely detectable levels after 48 h incubation. Although basal levels of TNF-alpha in the culture supernatants were increased after stimulation with PMA, neither pollutant alone nor combination with PMA affected the levels of TNF-alpha. These in vitro findings suggest that environmental pollutants may act as modulating factors of cutaneous inflammation by affecting the ability of keratinocytes to release pro-inflammatory cytokines.

Inhibition by beta-carotene of upper respiratory tumorigenesis in hamsters receiving diethylnitrosamine followed by cigarette smoke exposure

In recent intervention studies, beta-carotene failed to reduce or even increased the incidence of lung cancers in smokers. In the present investigation, the modifying effects of beta-carotene at various doses on the development of upper respiratory tract tumors were investigated in Syrian hamsters treated with diethylnitrosamine (DEN) and cigarette smoke. A total of 120 male 5-week-old hamsters were divided into 4 groups, each consisting of 30 animals. After a single subcutaneous (s.c.) injection of 100 mg/kg DEN, hamsters in groups 1-4 were respectively administered diets supplemented with beta-carotene at doses of 0.5%, 0.05%, 0.005% or 0% during experimental weeks 1 to 13, and simultaneously exposed to cigarette smoke. The duration of cigarette smoke exposure was 9 min twice a day, 5 days a week. Because of a marked reduction of body weight in group 1, the highest dose of beta-carotene was changed to 0.25% after 10 days. In all groups, epithelial hyperplasias and/or papillomas were induced in the larynx and trachea. However, the incidence and multiplicity of papillomas in group 1 were significantly (P < 0.05) lower than the group 4 values. Moreover, the beta-carotene treatments significantly (P < 0.05 or 0.01) reduced both the incidence and multiplicity of hyperplasias in a dose-dependent manner. The levels of retinol and beta-carotene in the serum, and the retinol level in the liver, were also elevated with dose dependence. Our results thus indicate that beta-carotene inhibits tumorigenesis, even at the high dose of 0.25%, under the present experimental conditions.

Experimental study of oxidative DNA damage

Animal experiments allow the study of oxidative DNA damage in target organs and the elucidation of dose-response relationships of carcinogenic and other harmful chemicals and conditions as well as the study of interactions of several factors. So far the effects of more than 50 different chemical compounds have been studied in animal experiments mainly in rats and mice, and generally with measurement of 8-oxodG with HPLC-EC. A large number of well-known carcinogens induce 8-oxodG formation in liver and/or kidneys. Moreover several animal studies have shown a close relationship between induction of dative DNA damage and tumour formation. In principle the level of oxidative DNA damage in an organ or cell may be studied by measurement of modified bases in extracted DNA by immunohistochemical visualisation, and from assays of strand breakage before and after treatment with repair enzymes. However, this level is a balance between the rates of damage and repair. Until the repair rates and capacity can be adequately assessed the rate of damage can only be estimated from the urinary excretion of repair products albeit only as an average of the entire body. A number of model compounds have been used to induce oxidative DNA damage in experimental animals. The hepatocarcinogen 2-nitropropane induces up to 10-fold increases in 8-oxodG levels in rat liver DNA. The level of 8-oxodG is also increased in kidneys and bone marrow but not in the testis. By means of 2-nitropropane we have shown correspondence between the increases in 8-oxodG in target organs and the urinary excretion of 8-oxodG and between 8-oxodG formation and the comet assay in bone marrow as well potent preventive effects of extracts of Brussels sprouts. Others have shown similar effects of green tea extracts and its components. Drawbacks of the use of 2-nitropropane as a model for oxidative DNA damage relate particularly to formation of 8-aminoguanine derivatives that may interfere with HPLC-EC assays and have unknown consequences. Other model compounds for induction of oxidative DNA damage, such as ferric nitriloacetate, iron dextran, potassium bromate and paraquat, are less potent and/or more organ specific. Inflammation and activation of an inflammatory response by phorbol esters or E. coli lipopolysaccharide (LPS) induce oxidative DNA damage in many target cells and enhance benzene-induced DNA damage in mouse bone marrow. Experimental studies provide powerful tools to investigate agents inducing and preventing oxidative damage to DNA and its role in carcinogenesis. So far, most animal experiments have concerned 8-oxodG and determination of additional damaged bases should be employed. An ideal animal model for prevention of oxidative DNA damage has yet to he developed.

High fat diet induced oxidative DNA damage estimated by 8-oxo-7,8-dihydro-2-deoxyguanosine excretion in rats

The role of dietary fats and energy in carcinogenesis has been partly related to oxidative damage to DNA. We have investigated the effect of dietary fat content and saturation on the urinary excretion of 8-oxo-7,8dihydro-2'-deoxyguanosine (8-oxodG) in male and female rats. Groups of Fischer F344 rats (n = 6-10) were fed control chow (3.4% fat) or diets containing 21.8% corn oil or 19.8% coconut oil + 2% corn oil for 12-15 weeks. At the end of the diet intervention period 24h urine was collected for determination of 8-oxodG by HPLC. In the male groups fed control, corn oil and coconut oil diet the excretion of 8-oxodG was 403+/-150, 932+/-198 and 954+/-367pmol/kg 24 h, respectively (p < 0.05). In the female groups fed control and corn oil diet the excretion of 8-oxodG was 752+/-80 and 2206+/-282 pmol/kg 24 h, respectively (p < 0.05). Calculated per whole animal the excretion was 137+/-51, 324+/-70 and 328+/-128 pmol/24 h in the control, corn and coconut oil male groups and 156+/-21 and 464+/-56 pmol/24 h in the control and corn oil female groups, respectively ( p < 0.05). Thus, per animal or per consumed energy there was much less difference in 8-oxodG excretion between the corresponding male and female groups and only significant difference between the high fat groups. There was a close correlation (r = 0.7; p < 0.05) between 8-oxodG excretion and the energy intake. The present study suggests that a high fat diet increases oxidative DNA modification substantially irrespective of the saturation level of the fat. Energy intake appears to be the major determinant of the rate of modification.

Analysis of environmental carcinogens associated with the incidence of lung cancer

It is presumed that carcinogens present in human lungs contribute to the incidence of lung cancer. Most of the carcinogens are inhaled in lung alveoli with particulate matter through the respiratory tract. On the basis of chemical analysis of 256 lung specimens with carcinomas resected in the period 1991 1996, the concentration of 1-nitropyrene (1-NP) was 19.7+/-10.5 pg/g of dry weight, and that of the dinitropyrenes (DNP) was 3.50+/-0.14-6.26+/-1.76. In addition, 2-nitrofluoranthene (NF) and 3-NF were detected at a higher level of 38.6+/-17.2 and 39.1+/-14.2, respectively, pg/g of dry weight. Concentrations of benzo[a]pyrene, benzo[e]pyrene, benzo[k]fluoranthene and benzo[ghi]perylene in 37 specimens collected in the period 1991 1996, were in the range of 138+/-82-399+/-220 pg/g of dry weight. No difference was found in the concentration of chemicals deposited in lung specimens from patients with lung cancer and tuberculosis as a control. By following the prognosis of 112 patients with carcinomas, we found that the deposition of 1-NP, 1,3-DNP, and 3-NF in lung tissues influenced their 5-year-survival after determination of chemicals. Lung specimens were divided into two groups of higher and lower chemical concentrations at the levels of 18 pg/g for 1-NP, 15 for 1,3-DNP, and 35 for 3-NF, and the findings were statistically analyzed by adjusting for age, gender, smoking status and cell type. The 5-year-survival of patients was markedly lower in the higher concentration group than the lower group.

Lung cancer patients have increased 8-hydroxydeoxyguanosine levels in peripheral lung tissue DNA

The 8-hydroxydeoxyguanosine (8-OH-dG) levels in the peripheral parts of human lung tissues were compared between lung cancer patients (n=70) and non-cancer patient controls (n=15). An increased level of 8-OH-dG was observed in the lung cancer group, in both the adenocarcinoma and non-adenocarcinoma (mainly squamous cell carcinoma) groups, as compared to the non-cancer control group. This result suggests that reactive oxygen species are partly involved in the induction of lung carcinomas (both adenocarcinoma and non-adenocarcinoma).

Formation of 8-hydroxydeoxyguanosine in rat kidney DNA after administration of N-ethyl-N-hydroxyethylnitrosamine

N-Ethyl-N-hydroxyethylnitrosamine (EHEN) is known to induce renal and liver tumors in rodents. Recent reports have indicated the formation of 8-hydroxydeoxyguanosine (8-OHdG), an oxidative DNA product, induced by various carcinogens. In the present study, to examine whether oxygen radicals are involved in tumorigenesis induced by EHEN, we investigated the formation and localization of 8-OHdG in kidney, liver and lung of rats. The effects of reduced glutathione (GSH) and diethylmaleate on these responses were also studied. Multiple doses of EHEN administrations (250, 500 or 750 mg/kg, i.p.) resulted in a significant elevation of the 8-OHdG level in kidney DNA in a dose-dependent manner and the formation of 8-OHdG reached the maximal level at 1-2 h after EHEN injection and recovered to the control level at 4 h. On the other hand, no increase in the 8-OHdG level was observed in the DNA of liver and lung. Combined pre- and post-treatment of rats with 2 x 800 mg/kg of GSH i.p. inhibited the elevation of the 8-OHdG level induced by EHEN. Pre-treatment with 0.3 ml/kg of diethylmaleate i.p. increased the formation of 8-OHdG. In the immunohistochemical examinations of rats treated with EHEN (750 mg/kg, i.p.), nuclear expression of 8-OHdG was detected in the epithelial cells of renal cortex, while no induction was observed in liver and lung. These findings suggest that the formation of 8-OHdG by active oxygen species may be an important factor in the initiation of EHEN-induced kidney carcinogenesis.

Analysis of a form of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine, as a marker of cellular oxidative stress during carcinogenesis

8-hydroxy-2'-deoxyguanosine (8-OH-dG) was first reported in 1984 as a major form of oxidative DNA damage product by heated sugar, Fenton-type reagents and X-irradiation in vitro. 8-OH-dG has been detected in cellular DNA using an HPLC-ECD method in many laboratories. Analyses of 8-OH-dG in animal organ DNA after the administration of oxygen radical-forming chemicals will be useful for assessments of their carcinogenic risk. Its analysis in human leucocyte DNA and in urine is a new approach to the assessment of an individual's cancer risk due to oxidative stress. The increase of the 8-OH-dG level in the cellular DNA, detected by HPLC-ECD method, was supported by its immunochemical detection and its enhanced repair activity. The validity of the general use of 8-OH-dG as a marker of cellular oxidative stress is discussed.

Murine strain differences in allergic airway inflammation and immunoglobulin production by a combination of antigen and diesel exhaust particles

To clarify the relationship between the manifestations of allergic airway inflammation modulated by diesel exhaust particles (DEP) and immunoglobulin production in response to an antigen, airway inflammation characterized by the infiltration of eosinophils, goblet cell proliferation, and antigen-specific immunoglobulin (Ig) production was investigated in five strains of mice after immunization with ovalbumin (OA). Mice were injected intratracheally with OA (1 microg) or OA (1 microg) + DEP (50 microg) four times at 3-week intervals. The order of antigen-specific IgG1 production in plasma of mouse strains treated with OA alone was CBA/2N <BDF/1 <C57BL/6 < ICR <C3H/He. The adjuvant effect of DEP on IgG1 production was observed in CBA/2N, BDF/1, ICR, and C57BL/6 mice. The immune activity in BDF/1 mice was significantly elevated (P < 0.01). The OA-specific IgE in plasma was unaffected by antigen challenge with or without DEP in any strain. The degree of eosinophilic inflammation and goblet cell proliferation in the airway induced by OA alone or OA + DEP corresponded well with the antigen-specific IgG1 production. These results suggest that the manifestations of allergic airway inflammation modulated by DEP were closely related to the immunoglobulin production response to OA, especially with regard to enhanced IgG1 production.