Formation of an oxidative DNA damage, 8-hydroxydeoxyguanosine, in mouse lung DNA after intratracheal instillation of diesel exhaust particles and effects of high dietary fat and beta-carotene on this process

8-Hydroxydeoxyguanosine in DNA from leukocytes of healthy adults: relationship with cigarette smoking, environmental tobacco smoke, alcohol and coffee consumption

8-Hydroxydeoxyguanosine (8-OHdG) has been widely used as a biomarker of oxidative DNA damage in both animal and human studies. However, controversial data exist on the relationship between 8-OHdG formation and age, sex and tobacco smoking in humans, while few or no data are available on other exposures such as environmental tobacco smoke, alcohol, coffee and tea consumption. We investigated the level of 8-OHdG in DNA from peripheral leukocytes among 102 healthy adults living in Brescia province, North Italy, aged 25-45 (mean: 35.2 years), of which 51 were males. 8-OHdG levels expressed as a ratio to total deoxyguanosine (8-OHdG/106 dG) in DNA showed wide interindividual variation, the highest value (63.8) being 6. 2-fold greater than the lowest (10.3). Current smokers showed lower mean 8-OHdG values than subjects who never smoked (29.3 and 34.0, respectively, p<0.05), and an inverse relationship was found between 8-OHdG and lifetime smoking, which was independent of age, sex and body mass index. An inverse relationship was also found with coffee drinking while no association was observed with alcohol and tea consumption, exposure to environmental tobacco smoke and use of vitamins in all subjects, and with use of oral contraceptives in females. The inverse relationship between smoking status and 8-OHdG levels could be explained by the presence of efficient repair processes for the oxidative damage induced by smoking. In this study, the smokers were relatively young (77% were less than 40 years) and only 7% smoked 30 or more cigarettes a day. In conclusion, it would appear that 8-OHdG levels in leukocytes may not provide a sensitive marker of exposure to tobacco smoking.

Dextran sulfate enhances the level of an oxidative DNA damage biomarker, 8-oxo-7,8-dihydro-2'-deoxyguanosine, in rat colonic mucosa

Dextran sodium sulfate (DSS) given in drinking water can induce colonic inflammation and produce colorectal tumors in rodents, although it is not directly genotoxic. The hypothesis that DSS can produce free radicals and induce oxidative DNA damage in colonic mucosa has been tested. In rats fed for 2 days with water containing 3% and 6% DSS, colonic inflammation manifestations were recorded and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a major biomarker of oxidative DNA damage, was assayed in colonic mucosa. As compared with control rats given pure water, inflammatory manifestations were seen in rats given DSS. At the same time, 8-oxodGuo levels in colonic mucosa were doubled (P < 0.001). These results suggest that formation of oxidative DNA damage in colonic mucosa depends on inflammation and maybe on the production of reactive oxygen species. This study shows that DSS can induce oxidative DNA damage within only 2 days, which could explain in part its carcinogenic properties.

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.

2-Hydroxyadenine, a mutagenic form of oxidative DNA damage, is not repaired by a glycosylase type mechanism in rat organs

Oxygen radicals are known to play a role in causing cellular DNA damage, which is involved in carcinogenesis. 8-Hydroxyguanine (8-OH-Gua) is a major form of oxidative DNA damage and is known as a useful marker of DNA oxidation. Recently, we found another type of oxidative DNA damage, 2-hydroxyadenine (2-OH-Ade), which has a mutation frequency comparable to that of 8-OH-Gua. We compared the repair activities for two types of oxidative DNA damage, 8-OH-Gua and 2-OH-Ade, in 7-week-old male Sprague-Dawley (SD) rat organs. The repair activities were measured by an endonuclease nicking assay using 22 mer [32P]-end-labeled double-stranded DNA substrates, which contained either 8-OH-Gua (opposite C) or 2-OH-Ade (opposite T or C). In all of the SD rat organs we studied, the nicking activity for 2-OH-Ade was not detected, while that for 8-OH-Gua was clearly detected with the same conditions. Moreover, the 2-OH-Ade nicking activity was not induced in Wistar rat kidney extracts prepared after ferric nitrilotriacetate (Fe-NTA) treatment, which is known to increase 8-OH-Gua repair activity. These results suggest that 2-OH-Ade might not be repaired by the glycosylase type mechanism in mammalian cells.

Urinary excretion of 5-(hydroxymethyl) uracil in healthy volunteers: effect of active and passive tobacco smoke

The urinary excretion of 5-(hydroxymethyl)uracil (5-HMUra), one of the major oxidative modifications of thymine, was investigated in 134 healthy volunteers living in North Italy. Overnight urine was collected, and a questionnaire was completed on smoking habits and exposure to environmental tobacco smoke (ETS). 5-HMUra was analyzed by GC/MS, following urine purification by HPLC. 5-HMUra excretion showed an approximately normal distribution, ranging from 0.08 to 0.84 (mean 0.44) nmoles/kg/8 hr and from 3.2 to 18.7 (mean 8.5) nmoles/mmoles creatinine. 5-HMUra excretion was significantly higher in women than in men and in smokers than in non-smokers when results were expressed as the ratio to creatinine. Slightly higher levels of 5-HMUra excretion, expressed as nmoles/mmoles creatinine, were also found in subjects highly exposed to ETS, monitored either as the number of hours of exposure or as the number of smokers in the workplace and at home. Our results show that the urinary excretion of 5-HMUra is higher than that of other oxidized nucleobases, including 8-oxo-7,8-dihydroguanine, and can be slightly modified by environmental factors such as tobacco smoke. These findings suggest that measurement of urinary excretion of 5-HMUra could be useful as a biomarker of oxidative DNA damage and repair, though further research is needed to support these data.

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).

Effects of forced and spontaneous exercise on 8-hydroxydeoxyguanosine levels in rat organs

We investigated the effects of forced and spontaneous exercise on the levels of 8-hydroxydeoxyguanosine (8-OH-dG), a form of oxidative DNA damage, in rat organs (heart, lung, and liver). Rats were randomly assigned to one of three groups: forced exercise group (F), spontaneous exercise group (S), and sedentary control group (C). The mean levels of 8-OH-dG in the F group were 1.9-, 2.1-, and 2.4-fold higher in the heart, lung, and liver DNA, respectively, than in the S group. In the S group of rats, the distance run was not significantly correlated to the 8-OH-dG levels in the heart, lung, and liver DNA. These results demonstrate that the intensity of exercise is an important determinant in DNA damage, and suggest that spontaneous physical exercise is beneficial for maintaining a low level of oxidative DNA damage.

Melatonin reduces the increase in 8-hydroxy-deoxyguanosine levels in the brain and liver of kainic acid-treated rats

In the present study, the effect of melatonin on oxidative DNA damage induced by kainic acid (KA) treatment was investigated. 8-hydroxy-deoxyguanosine (8-OH-dG) is a main product of oxidatively damaged DNA and was used as the endpoint in these studies. The levels of 8-OH-dG were found to be elevated in the hippocampus and frontal cortex of rats treated with KA. These elevated levels were significantly reduced in animals that were co-treated with melatonin. Thus, there was no difference in 8-OH-dG levels in the brain of control rats compared to those treated with KA (10 mg/kg) plus melatonin (10 mg/kg). The levels of 8-OH-dG also increased in the liver of rats treated with KA. This rise in oxidatively damaged DNA was also prevented by melatonin administration. Melatonin's ability to reduce KA-induced increases in neural and hepatic 8-OH-dG levels presumably relates to its direct free radical scavenging ability and possibly to other antioxidative actions of melatonin.

Lung tumor induced by long-term inhalation or intratracheal instillation of diesel exhaust particles

A series of long-term inhalation studies of diesel exhaust and intratracheal instillation of diesel particles was conducted on female SPF F344 rats. A particulate but not gaseous component in the inhalation studies provoked inflammatory changes and tumors in the lung, and the intratracheally instilled particles showed similar findings. Adenoma and adenocarcinoma were the main histologic types of the tumors which developed and they showed the phenotype of surfactant apoprotein-producing cells, suggesting that the tumor cell origin was a Type II alveolar cell. The tumor incidence rate correlated with the cumulative concentration of inhaled particles per week and with the amount of particles deposited in the lung. In the instillation studies, the carbon core of diesel particles obtained after exhaustive extraction of tarry matter showed a slightly lower positive rate of lung tumor formation than the rate in untreated diesel particles, indicating an important role of carbon core in the diesel particle-induced tumor. In the intratracheal instillation studies, point mutation of K-ras oncogene was detected in a significant percentage in the tumor cells.

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.

8-hydroxyguanine (7,8-dihydro-8-oxoguanine) DNA glycosylase and AP lyase activities of hOGG1 protein and their substrate specificity

Recently we cloned a structural human homolog (hOGG1) of the yeast OGG1 (yOGG1) gene that is involved in the excision repair of 8-hydroxyguanine (also known as 7,8-dihydro-8-oxoguanine; oh8Gua), hOGG1 protein shares 38% amino acid identity with yOGG1 protein. In this paper, we define the substrate specificity of oh8Gua DNA glycosylase and AP lyase activities of the hOGG1 protein. The oh8Gua released from oh8Gua containing DNA was measured by analysis with HPLC coupled with electrochemical detector (ECD) and cleavage sites in the DNA were identified by cleavage assay using gel electrophoresis. GST-hOGG1 protein possessed the oh8Gua DNA glycosylase/AP lyase activity and weak delta-elimination activity, oh8Gua opposite the C in duplex oligonucleotide was most efficiently released by GST-hOGG1 protein and oh8Gua opposite the T was also released, while oh8Gua opposite the G or A was very slowly done. The rank order of DNA cleavage efficiency was the same as that of oh8Gua glycosylase activity. Glycosylase/AP lyase activities and their substrate specificities of the GST-hOGG1 protein was similar to GST-yOGG1 protein but different from MutM protein. These results indicate that the dominant function of hOGG1 protein is a oh8Gua glycosylase reaction by specifically recognizing oh8Gua and pyrimidine opposite the oh8Gua and delta-elimination reaction in the same manner as yOGG1 protein. Thus, the hOGG1 gene is a functional human homolog of the yOGG1 gene on oh8Gua excision repair in spite of the low structural identity at amino acid level between hOGG1 and yOGG1 proteins.

Presence of human cellular protein(s) that specifically binds and cleaves 8-hydroxyguanine containing DNA

8-hydroxyguanine (oh8Gua) is a major form of oxygen free radical-induced DNA damage. The oh8Gua nucleotide can pair with cytosine (C) and adenine (A) nucleotides which can cause G:C to T:A transversions. It is known that multiple repair systems for the correction of the oh8Gua exist in both mammalian and bacterial cells. Using the technique of gel mobility shift assay, protein(s) bound to the oh8Gua:C base pair in short fragments of DNA was detected in cell-free extracts of a human small-cell lung cancer cell line. This DNA binding activity was specific, since it was poorly detected with an unmodified G:C base pair containing oligonucleotide duplex and was affected by neither the unmodified G:C base pair nor an oh8Gua:A base pair containing oligonucleotide duplex. The partially purified protein which selectively binds to the oh8Gua:C base pair was shown by gel filtration column chromatography to have an apparent molecular mass of 52 kDa. The column fraction which showed the highest binding activity to the oh8Gua:C base pair was found to possess an enzymatic activity that specifically cleaves the oh8Gua containing oligonucleotide strand at both the 5' and 3' sides of the oh8Gua residue. These results indicate the presence of a protein(s) that is involved in a DNA repair pathway for the correction of the oh8Gua residue in human cells.

Generation of reactive oxygen species during interaction of diesel exhaust particle components with NADPH-cytochrome P450 reductase and involvement of the bioactivation in the DNA damage

Since the toxicity of diesel exhaust particles (DEP) after intratracheal injection, was suppressed by pretreatment with superoxide dismutase (SOD) modified with polyethylene glycol (Sagai et al. Free Rad. Biol. Med. 14: 37-47; 1993), the possibility that superoxide could be enzymatically and continuously generated from diesel exhaust particles (DEP), was examined. Nicotinamide-adenine dinucleotide phosphate, reduced (NADPH) oxidation was stimulated during interaction of a methanol extract of DEP with the Triton N-101 treated microsomal preparation of mouse lung whereas the cytosolic fraction was less active, suggesting that DEP contains substrates for NADPH-cytochrome P450 reductase (EC 1.6.2.4, P450 reductase) rather than DT-diaphorase. When purified P450 reductase was used as the enzyme source, the turnover value was enhanced approximately 260-fold. Quinones appeared to be served as substrate for P450 reductase because reaction was inhibited by addition of glutathione (GSH) to form those GSH adduct or pretreatment with NaBH4 to reduce those to the hydroxy compounds although a possibility of nitroarenes as the alternative substrates cannot be excluded. A methanol extract of DEP (37.5 micrograms) caused a significant formation of superoxide (3240 nmol/min/mg protein) in the presence of P450 reductase. Electron spin resonance (ESR) experiments revealed that hydroxyl radical was formed as well. The reactive species generated by DEP in the presence of P450 reductase caused DNA scission which was reduced in the presence of superoxide dismutase (SOD), catalase, or hydroxyl radical scavenging agents. Taken together, these results indicate that DEP components, probably quinoid or nitroaromatic structures, that appear to promote DNA damage through the redox cycling based generation of superoxide.

Aromatic hydroxylation in nasal lavage fluid following ambient ozone exposure

Ozone at ambient concentrations affects lung function and initiates an inflammatory response of the airways. However, the underlying mechanisms are poorly understood. In vitro studies have shown that ozone reacts with water to give reactive hydroxyl radicals capable of oxidizing a wide range of biomolecules. We conducted a study to determine if in vivo hydroxyl radical attack on human airways occurs under natural exposure to ozone. The relation of orthotyrosine to para-tyrosine as a measure of hydroxyl radical attack was analyzed in nasal lavage samples of 44 primary school children in an epidemiologic study. Repeated nasal lavages were performed between May and October 1991 both following "low" (daily half-hour maximum < 140 micrograms/m3, approximately 70 ppb) and "high" (daily half-hour maximum > 180 micrograms/m3, approximately 90 ppb) ozone exposure. Concomitantly, lung function tests were performed. On average, 11.6 (6-16) nasal lavages were performed for each of 24 study days (10 days following "low" ozone exposure and 14 days following "high" ozone exposure). Average ortho-tyrosine (median; 5-95% percentile) for each child was 0.037 mumol/L (0.016-0.064 mumol/L) and average para-tyrosine was 15.7 mumol/L (9.8-24.1 mumol/L). Ortho-tyrosine (as percentage of tyrosine) was significantly higher following days with "high" ozone exposure (0.18%) vs. days following "low" ozone exposure (0.02%; p = .0001). Ortho-tyrosine showed an inverse relationship with forced vital capacity (p = .01) but was not related to inflammation of the upper airways as assessed by cell counts of polymorphonuclear neutrophils. Hydroxyl radical attack subsequent to ambient ozone occurs in the upper airways of healthy children and is related to lung function decrements.

Cancer risk and oxidative DNA damage in man

In living cells reactive oxygen species (ROS) are formed continuously as a consequence of metabolic and other biochemical reactions as well as external factors. Some ROS have important physiological functions. Thus, antioxidant defense systems cannot provide complete protection from noxious effects of ROS. These include oxidative damage to DNA, which experimental studies in animals and in vitro have suggested are an important factor in carcinogenesis. Despite extensive repair oxidatively modified DNA is abundant in human tissues, in particular in tumors, i.e., in terms of 1-200 modified nucleosides per 10(5) intact nucleosides. The damaged nucleosides accumulate with age in both nuclear and mitochondrial DNA. The products of repair of these lesions are excreted into the urine in amounts corresponding to a damage rate of up to 10(4) modifications in each cell every day. The most abundant of these lesions, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), is also the most mutagenic, resulting in GT transversions which are frequently found in tumor relevant genes. A series of other oxidative modifications of base and sugar residues occur frequently in DNA, but they are less well studied and their biological significance less apparent. The biomarkers for study of oxidative DNA damage in humans include urinary excretion of oxidized nucleosides and bases as repair products and modifications in DNA isolated from target tissue or surrogate cells, such as lymphocytes. These biomarkers reflect the rate of damage and the balance between the damage and repair rate, respectively. By means of biomarkers a number of important factors have been studied in humans. Ionizing radiation, a carcinogenic and pure source of ROS, induced both urinary and leukocyte biomarkers of oxidative DNA damage. Tobacco smoking, another carcinogenic source of ROS, increased the oxidative DNA damage rate by 35-50% estimated from the urinary excretion of 8-oxodG, and the level of 8-oxodG in leukocytes by 20-50%. The main endogenous source of ROS, the oxygen consumption, showed a close correlation with the 8-oxodG excretion rate although moderate exercise appeared to have no immediate effect. So far, cross-sectional study of diet composition and intervention studies, including energy restriction and antioxidant supplements, have generally failed to show an influence on the oxidative DNA modification. However, a diet rich of Brussels sprouts reduced the oxidative DNA damage rate, estimated by the urinary excretion of 8-oxodG, and the intake of vitamin C was a determinant for the level of 8-oxodG in sperm DNA. A low-fat diet reduced another marker of oxidative DNA damage in leukocytes. In patients with diseases associated with a mechanistically based increased risk of cancer, including Fanconi anemia, chronic hepatitis, cystic fibrosis, and various autoimmune diseases, the biomarker studies indicate an increased rate of oxidative DNA damage or in some instances deficient repair. Human studies support the experimentally based notion of oxidative DNA damage as an important mutagenic and apparently carcinogenic factor. However, the proof of a causal relationship in humans is still lacking. This could possibly be supported by demonstration of the rate of oxidative DNA damage as an independent risk factor for cancer in a prospective study of biobank material using a nested case control design. In addition, oxidative damage may be important for the aging process, particularly with respect to mitochondrial DNA and the pathogenesis of inflammatory diseases.

Cancer risk and oxidative DNA damage in man

In living cells reactive oxygen species (ROS) are formed continuously as a consequence of metabolic and other biochemical reactions as well as external factors. Some ROS have important physiological functions. Thus, antioxidant defense systems cannot provide complete protection from noxious effects of ROS. These include oxidative damage to DNA, which experimental studies in animals and in vitro have suggested are an important factor in carcinogenesis. Despite extensive repair oxidatively modified DNA is abundant in human tissues, in particular in tumors, i.e., in terms of 1-200 modified nucleosides per 10(5) intact nucleosides. The damaged nucleosides accumulate with age in both nuclear and mitochondrial DNA. The products of repair of these lesions are excreted into the urine in amounts corresponding to a damage rate of up to 10(4) modifications in each cell every day. The most abundant of these lesions, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), is also the most mutagenic, resulting in GT transversions which are frequently found in tumor relevant genes. A series of other oxidative modifications of base and sugar residues occur frequently in DNA, but they are less well studied and their biological significance less apparent. The biomarkers for study of oxidative DNA damage in humans include urinary excretion of oxidized nucleosides and bases as repair products and modifications in DNA isolated from target tissue or surrogate cells, such as lymphocytes. These biomarkers reflect the rate of damage and the balance between the damage and repair rate, respectively. By means of biomarkers a number of important factors have been studied in humans. Ionizing radiation, a carcinogenic and pure source of ROS, induced both urinary and leukocyte biomarkers of oxidative DNA damage. Tobacco smoking, another carcinogenic source of ROS, increased the oxidative DNA damage rate by 35-50% estimated from the urinary excretion of 8-oxodG, and the level of 8-oxodG in leukocytes by 20-50%. The main endogenous source of ROS, the oxygen consumption, showed a close correlation with the 8-oxodG excretion rate although moderate exercise appeared to have no immediate effect. So far, cross-sectional study of diet composition and intervention studies, including energy restriction and antioxidant supplements, have generally failed to show an influence on the oxidative DNA modification. However, a diet rich of Brussels sprouts reduced the oxidative DNA damage rate, estimated by the urinary excretion of 8-oxodG, and the intake of vitamin C was a determinant for the level of 8-oxodG in sperm DNA. A low-fat diet reduced another marker of oxidative DNA damage in leukocytes. In patients with diseases associated with a mechanistically based increased risk of cancer, including Fanconi anemia, chronic hepatitis, cystic fibrosis, and various autoimmune diseases, the biomarker studies indicate an increased rate of oxidative DNA damage or in some instances deficient repair. Human studies support the experimentally based notion of oxidative DNA damage as an important mutagenic and apparently carcinogenic factor. However, the proof of a causal relationship in humans is still lacking. This could possibly be supported by demonstration of the rate of oxidative DNA damage as an independent risk factor for cancer in a prospective study of biobank material using a nested case control design. In addition, oxidative damage may be important for the aging process, particularly with respect to mitochondrial DNA and the pathogenesis of inflammatory diseases.

Biological effects of diesel exhaust particles (DEP). II. Acute toxicity of DEP introduced into lung by intratracheal instillation

Histopathological examination and cytological analyses in bronchial alveolar lavage fluids (BALF) were performed to clarify the acute toxicity of diesel exhaust particles (DEP) introduced into the lung of ICR mice by intratracheal instillation. Activated charcoal (Norit) was intratracheally administered as a control for non-oedemagenic carbon particles. After administration of two doses (0.4 mg or 0.8 mg per mouse) of DEP, lung water contents increased with instillation dose and with time and increased 1.9 and 2.7-fold, respectively, compared to control animals 24 h after the administration of DEP. In contrast, the instillation of Norit had no effect on the increase in water contents. An inflammatory response in lungs was observed by an increase of inflammatory cells in BALF from mice instilled with DEP. The degree of increase in neutrophils of BALF from mice treated with DEP was much greater than in mice treated with Norit. An intense color of MB-pigment, which showed the extent and degree of endothelial cell injury, was found up to 4 h after administration of DEP. Histopathologically, the disruption of capillary endothelial cells, the detachment from their basement membrane and necrosis, disruption and desquamation of type I pneumocytes were observed, 6 h after the injection of DEP, by electron microscopy. An influx of neutrophils into alveoli, intra-alveolar hemorrhage, perivascular oedema and bronchiolar cell hypertrophy were detected between 18 and 24 h after DEP administration. However, the magnitude of these appearances was greater in mice treated with 0.8 mg of DEP than in mice treated with 0.4 mg. The administration of Norit caused an increase of alveolar macrophages and slight infiltration of neutrophils into the alveolar air spaces and alveolar septa in the animals and had no effects on the bronchioles. These results may suggest that damage of capillary endothelial cells and type I pneumocytes are the earliest changes of lung toxicities by DEP and these cell injuries lead to alveolar oedema and the subsequent inflammatory response.