Long-range oxidative damage to DNA: effects of distance and sequence.
INTRODUCTION: Oxidative damage to DNA in vivo can lead to mutations and cancer. DNA damage and repair studies have not yet revealed whether permanent oxidative lesions are generated by charges migrating over long distances. Both photoexcited *Rh(III) and ground-state Ru(III) intercalators were previously shown to oxidize guanine bases from a remote site in oligonucleotide duplexes by DNA-mediated electron transfer. Here we examine much longer charge-transport distances and explore the sensitivity of the reaction to intervening sequences. RESULTS: Oxidative damage was examined in a series of DNA duplexes containing a pendant intercalating photooxidant. These studies revealed a shallow dependence on distance and no dependence on the phasing orientation of the oxidant relative to the site of damage, 5'-GG-3'. The intervening DNA sequence has a significant effect on the yield of guanine oxidation, however. Oxidation through multiple 5'-TA-3' steps is substantially diminished compared to through other base steps. We observed intraduplex guanine oxidation by tethered *Rh(III) and Ru(III) over a distance of 200 A. The distribution of oxidized guanine varied as a function of temperature between 5 and 35 degrees C, with an increase in the proportion of long-range damage (> 100 A) occurring at higher temperatures. CONCLUSIONS: Guanines are oxidized as a result of DNA-mediated charge transport over significant distances (e.g. 200 A). Although long-range charge transfer is dependent on distance, it appears to be modulated by intervening sequence and sequence-dependent dynamics. These discoveries hold important implications with respect to DNA damage in vivo. (+info
Exposure to nitrogen dioxide and the occurrence of bronchial obstruction in children below 2 years.
BACKGROUND: The objective of the investigation was to test the hypothesis that exposure to nitrogen dioxide (NO2) has a causal influence on the occurrence of bronchial obstruction in children below 2 years of age. METHODS: A nested case-control study with 153 one-to-one matched pairs was conducted within a cohort of 3754 children born in Oslo in 1992/93. Cases were children who developed > or = 2 episodes of bronchial obstruction or one episode lasting >4 weeks. Controls were matched for date of birth. Exposure measurements were performed in the same 14-day period within matched pairs. The NO2 exposure was measured with personal samplers carried close to each child and by stationary samplers outdoors and indoors. RESULTS: Few children (4.6%) were exposed to levels of NO2 > or = 30 microg/m3 (average concentration during a 14-day period). In the 153 matched pairs, the mean level of NO2 was 15.65 microg/m3 (+/-0.60, SE) among cases and 15.37 (+/-0.54) among controls (paired t = 0.38, P = 0.71). CONCLUSIONS: The results suggest that NO2 exposure at levels observed in this study has no detectable effect on the risk of developing bronchial obstruction in children below 2 years of age. (+info
Airway inflammatory response to ozone in subjects with different asthma severity.
The aim of this study was to evaluate whether ozone exposure induces a similar airway inflammatory response in subjects with different degrees of asthma severity. Two groups of asthmatic subjects were studied: seven with intermittent mild asthma not requiring regular treatment (group A); and seven with persistent mild asthma requiring regular treatment with inhaled corticosteroids and long-acting beta2-agonists (group B). All subjects were exposed, in a randomized cross-over design, to air or O3 (0.26 parts per million (ppm) for 2 h with intermittent exercise); subjects in group B withdrew from regular treatment 72 h before each exposure. Before the exposure, and 1 and 2 h after the beginning of the exposure they performed a pulmonary function test, and a questionnaire was completed to obtain a total symptom score (TSS). Six hours after the end of the exposure, hypertonic saline (HS) sputum induction was conducted. Sputum cell percentages, eosinophil cationic protein (ECP) and interleukin (IL)-8 concentrations in the sputum supernatant were measured. TSS significantly increased and forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) significantly decreased after O3 exposure in comparison with air exposure in group A, whereas no changes were observed in group B except for a significant decrement of FEV1 2 h after the beginning of O3 exposure. Sputum neutrophil percentage was significantly higher after O3 exposure than after air exposure in both groups (Group A: 70.2% (28-87) versus 26.6% (8.6-73.2); Group B: 62.1% (25-82.4) versus 27.9% (14.4-54)). IL-8 was higher in sputum supernatant collected 6 h after O3 exposure than after air, only in group A. No change due to O3 has been found in sputum eosinophil percentage and ECP concentration in both groups. In conclusion, the degree of airway response to a short-term exposure to ozone is different in subjects with asthma of different severity. The available data do not allow elucidation of whether this difference depends on the severity of the disease or on the regular anti-inflammatory treatment. (+info
Capsaicin-sensitive C-fiber-mediated protective responses in ozone inhalation in rats.
To assess the role of lung sensory C fibers during and after inhalation of 1 part/million ozone for 8 h, we compared breathing pattern responses and epithelial injury-inflammation-repair in rats depleted of C fibers by systemic administration of capsaicin as neonates and in vehicle-treated control animals. Capsaicin-treated rats did not develop ozone-induced rapid, shallow breathing. Capsaicin-treated rats showed more severe necrosis in the nasal cavity and greater inflammation throughout the respiratory tract than did control rats exposed to ozone. Incorporation of 5-bromo-2'-deoxyuridine (a marker of DNA synthesis associated with proliferation) into terminal bronchiolar epithelial cells was not significantly affected by capsaicin treatment in rats exposed to ozone. However, when normalized to the degree of epithelial necrosis present in each rat studied, there was less 5-bromo-2'-deoxyuridine labeling in the terminal bronchioles of capsaicin-treated rats. These observations suggest that the ozone-induced release of neuropeptides does not measurably contribute to airway inflammation but may play a role in modulating basal and reparative airway epithelial cell proliferation. (+info
Effect of ultrasonically nebulized distilled water on airway epithelial cell swelling in guinea pigs.
To investigate the pathogenesis of ultrasonically nebulized distilled water-induced airway narrowing, we studied the role of airway epithelial cells during a distilled water-inhalation challenge in an animal model of airway inflammation. Guinea pigs were divided into four groups: 1) a sham/saline (S/S) group: sham ozone followed by saline inhalation; 2) a sham/water (S/W) group: sham ozone followed by water inhalation; 3) an ozone/saline (O/S) group: ozone followed by saline inhalation; and 4) an ozone/water (O/W) group: ozone followed by water inhalation. After exposure to either 3.0 parts/million ozone or air at the same flow rate for 2 h, guinea pigs were anesthetized and tracheostomized, and then lung resistance (RL) was measured. For morphometric assessment, tissues were fixed with formaldehyde, stained with hematoxylin and eosin, and cut into transverse sections. Airway dimensions were either measured directly or calculated from the internal perimeter, the external perimeter, and airway wall area. There were no statistical differences in the values of RL before distilled water inhalation between the sham groups and the ozone groups. RL increased significantly after 10 min of distilled water inhalation in both the S/W group and the O/W group. In the S/W group, epithelial cells were swollen, and intercellular spaces were wider, resulting in significant increase in epithelial wall thickness, but there was no significant infiltration by inflammatory cells. In the O/S group, the epithelium showed infiltration by inflammatory cells without change in cell volume. In the O/W group, the epithelium showed both infiltration and a greater increase in epithelial wall thickness compared with the S/W group. These results suggest that airway epithelial cell swelling, induced by inhaled distilled water, increases with RL in guinea pigs and that this reaction may be accelerated by airway inflammation. (+info
Personally measured weekly exposure to NO2 and respiratory health among preschool children.
Nitrogen dioxide is known as a deep lung irritant. The aim of this study was to find out whether the relatively low ambient air NO2 concentrations in the northern city of Helsinki had an impact on the respiratory health of children. The association between personal exposure to ambient air NO2 and respiratory health was investigated in a 13-week follow-up study among 163 preschool children aged 3-6 yrs. Personal weekly average exposure to NO2 was measured by passive diffusion samplers attached to the outer garments. Symptoms were recorded daily in a diary by the parents. Among 53 children, peak expiratory flow (PEF) was measured at home in the mornings and evenings. The association between NO2 exposure and respiratory symptoms was examined with Poisson regression. The median personal NO2 exposure was 21.1 microg x m(-3) (range 4-99 microg x m(-3)). An increased risk of cough was associated with increasing NO2 exposure (risk ratio = 1.52; 95% confidence interval 1.00-2.31). There was no such association between personal weekly NO2 exposure and nasal symptoms, but a nonsignificant negative association was found between the exposure and the weekly average deviation in PEF. In conclusion, even low ambient air NO2 concentrations can increase the risk of respiratory symptoms among preschool children. (+info
Ozone-induced lung function decrements do not correlate with early airway inflammatory or antioxidant responses.
This study sought to clarify the early events occurring within the airways of healthy human subjects performing moderate intermittent exercise following ozone challenge. Thirteen healthy nonsmoking subjects were exposed in a single blinded, crossover control fashion to 0.2 parts per million (ppm) O3 and filtered air for 2 h, using a standard intermittent exercise and rest protocol. Lung function was assessed pre- and immediately post-exposure. Bronchoscopy was performed with endobronchial mucosal biopsies, bronchial wash (BW) and bronchoalveolar lavage (BAL) 1.5 h after the end of the exposure period. Respiratory tract lining fluid (RTLF) redox status was assessed by measuring a range of antioxidants and oxidative damage markers in BW and BAL fluid samples. There was a significant upregulation after O3 exposure in the expression of vascular endothelial P-selectin (p<0.005) and intercellular adhesion molecule-1 (p<0.005). This was associated with a 2-fold increase in submucosal mast cells (p<0.005) in biopsy samples, without evidence of neutrophilic inflammation, and a decrease in BAL fluid macrophage numbers (1.6-fold, p<0.005), with an activation of the remaining macrophage subset (2.5-fold increase in % human leukocyte antigen (HLA)-DR+ cells, p<0.005). In addition, exposure led to a 4.5-fold and 3.1-fold increase of reduced glutathione (GSH) concentrations, in BW and BAL fluid respectively (p<0.05), with alterations in urate and alpha-tocopherol plasma/RTLF partitioning ratios (p<0.05). Spirometry showed reductions in forced vital capacity (p<0.05) and forced expiratory volume in one second (p<0.01), with evidence of small airway narrowing using forced expiratory flow values (p<0.005). Evidence was found of O3-induced early adhesion molecule upregulation, increased submucosal mast cell numbers and alterations to the respiratory tract lining fluid redox status. No clear relationship was demonstrable between changes in these early markers and the lung function decrements observed. The results therefore indicate that the initial lung function decrements are not predictive of, or causally related to the O3-induced inflammatory events in normal human subjects. (+info
Antioxidant consumption and repletion kinetics in nasal lavage fluid following exposure of healthy human volunteers to ozone.
To obtain information on the real-time events occurring within human respiratory tract lining fluids (RTLFs) during ozone exposure, sequential nasal lavage was performed on 13 human volunteers exposed on separate occasions to 0.2 parts per million O3 and filtered air (2-h exposures, with intermittent exercise). Nasal lavage was performed and blood samples obtained at four time points throughout each exposure: pre-exposure (Pre-E), 1 h into exposure (1h-E), immediately post-exposure (0h-PE) and 1 h post-exposure (1h-PE). Endobronchial mucosal biopsies were obtained at 1.5 h-post exposure (1.5h-PE). Nasal RTLF neutrophilia was not apparent during, or 1.5 h after, 03 exposure. Furthermore, activation of the pre-existing neutrophil population did not occur. Airway permeability was not altered by this 03 exposure regimen. Sequential lavage resulted in significant washout of RTLF ascorbic acid, reduced glutathione, extracellular superoxide dismutase and myeloperoxidase at 1h-E, 0h-PE and 1.5h-PE relative to baseline Pre-E values. In contrast, RTLF uric acid (UA), total protein and albumin concentrations did not display washout kinetics. Of the antioxidants examined, only UA was clearly depleted by 03, concentrations, falling by 6.22 micromol x L(-1) at 1h-E, compared with 1.61 micromol x L(-1) (p<0.01) during control air exposure. The establishment of a new pseudo-steady-state concentration of RTLF UA (70% of Pre-E values) during the second hour of O3 exposure was coincident with a small but significant increase in plasma UA concentration (19.27 (O3) versus 1.95 micromol x L(-1) (air), p<0.05). These data demonstrate that inhalation of 0.2 parts per million 03 results in the depletion of nasal respiratory tract lining fluid uric acid and that this regional loss of uric acid leads to a small increase in plasma uric acid concentration. Whilst the reaction of uric acid with inspired 03 may confer protection locally, the role of upper airway uric acid as a sink for inhaled O3 is not supported by these findings. (+info