Products of ozonized arachidonic acid potentiate the formation of DNA single strand breaks in cultured human lung cells

Suppression of lipid hydroperoxide-induced oxidative damage to cellular DNA by esculetin

Linoleic acid hydroperoxide (LOOH) has been reported to cause an increase in the content of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a typical oxidation product of DNA bases, in cultured cells due to coexisting iron(III) ion. We examined whether coumarins are able to suppress the formation of 8-oxodG in the DNA of human diploid fibroblasts, TIG-7 cells, treated with LOOH and iron(III) ion. Cotreatment of TIG-7 cells with esculetin (6,7-dihydroxycoumarin) significantly suppressed the increase in 8-oxodG content induced by LOOH and iron(III) ion. Pretreatment of cells with esculetin for 24 h was also effective in protecting cellular DNA against oxidative damage induced by subsequent treatment with LOOH and iron(III) ion. Pretreatment with esculin, the 6-glucoside of esculetin, was effective, but to a lesser extent. Furthermore, the free radical-scavenging activities of coumarins and hydroxycinnamic acids were examined by measuring the inhibition of spin-adduct formation of hydroxyl radicals with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Compounds bearing an ortho-catechol moiety, such as esculetin, fraxetin, and caffeic acid, significantly reduced the ESR signal intensities of the DMPO-OH spin adduct. These results indicate that esculetin is effective in protecting cells against DNA damage induced by oxidative stress and that the presence of an ortho-catechol moiety is important for antioxidant activities against reactive oxygen species.

Formation of 8-oxo-2'-deoxyguanosine in the DNA of human diploid fibroblasts by treatment with linoleic acid hydroperoxide and ferric ion

Lipid peroxides are suggested to be related to the occurrence of a variety of diseases including cancer and atherosclerosis. We examined whether lipid peroxides cause oxidative damage to DNA in intact cells. Linoleic acid hydroperoxide (LOOH) and ferric chloride were used at concentrations at which separate treatment had no effect on the formation of 8-oxo-2'-deoxyguanosine (8-oxodG) in DNA or the survival rate of cultured human diploid fibroblasts, TIG-7. The amount of 8-oxodG in the cellular DNA increased significantly when TIG-7 cells were treated concurrently with LOOH and ferric chloride. In a LOOH concentration-dependent manner 8-oxodG was formed. However, no significant induction of the activities of superoxide dismutases, catalase, or glutathione peroxidase was observed under these conditions. The formation of 8-oxodG by lipid hydroperoxides seems to be due to the generation of reactive species other than superoxide radicals and hydrogen peroxide. These results indicate that some species formed during the reaction of lipid hydroperoxides with ferric ion can cause oxidative damage to DNA.

Mechanisms of pollution-induced airway disease: in vitro studies in the upper and lower airways

Evidence from both epidemiological and laboratory-based studies suggests that increased exposure to liquid petroleum and gas-derived air pollutants [nitrogen dioxide (NO2), ozone, and respirable particulate matter] may play a role in the clinical manifestation of both allergic and non-allergic airway disease. The mechanisms and cell types involved in pollutant-mediated effects in the airways, however, are not clear. In vitro studies have suggested that human fibroblasts, B-lymphocytes, alveolar macrophages, and epithelial cells/cell lines may be involved. Studies of fibroblasts and macrophages have demonstrated that exposure to ozone results in decreased cell viability and increased release of pro-inflammatory mediators from macrophages. Similarly, studies of B-lymphocytes have demonstrated that exposure to diesel exhaust particles (DEP) enhances the synthesis of immunoglobulin E by these cells. The airway epithelial cells have received the greatest attention in mechanistic studies of air pollution-induced airway disease and suggest that these cells are likely to play a pivotal role in the pathogenesis of airways disease. Various studies have demonstrated that exposure of nasal or bronchial epithelial cells to NO2, ozone, and DEP results in significant synthesis and release of pro-inflammatory mediators, including eicosanoids, cytokines, and adhesion molecules. Additionally, evidence suggests that epithelial cells of atopic individuals release significantly greater amounts of cytokines such as granulocyte-macrophage colony stimulating factor (GM-CSF), interleukin-6 (IL-6), IL-8, and regulated on activation, normal T-cell expressed and secreted (RANTES), on exposure to NO2 and ozone. Studies investigating the biological relevance of epithelial cell-derived pro-inflammatory mediators have shown that these enhance eosinophil chemotaxis and eosinophil adherence to endothelial cells, suggesting that pollution-induced inflammation of the airways is likely to be influenced by modulation of epithelial synthesis and release of these mediators.

DNA damage in nasal respiratory epithelium from children exposed to urban pollution

The nasal cavity is the most common portal of entry to the human body and a well-known target site for a wide range of air pollutants and chemically induced toxicity and carcinogenicity. DNA single-strand breaks (SSB) can be used as a biomarker of oxidant exposure and as an indicator of the carcinogenicity and mutagenicity of a substance. We examined the utility of using the alkaline single cell gel electrophoresis assay (SCGE) for measuring DNA damage in children's nasal epithelium exposed to air pollutants. We studied 148 children, ages 6-12, including 19 control children from a low polluted Pacific port and 129 children from Southwest Metropolitan Mexico City, an urban polluted area with high ozone concentrations year-round. Three sets of two nasal biopsies were taken in a 3-month period. All exposed children had upper respiratory symptoms and DNA damage in their nasal cells. Eleven- and twelve-year-olds had the most DNA damage, and more than 30% of children aged 9-12 exhibited patchy areas of squamous metaplasia over high-flow nasal regions. These areas had the greatest numbers of damaged DNA cells (P < or = 0.001) and a large number of DNA tails > 80 microns (P < 0.001) when compared to the contralateral macroscopically normal site in the same child. The youngest children with significantly less outdoor exposure displayed patchy areas of goblet cell hyperplasia and had the least DNA damage. These findings suggest that SCGE can be used to monitor DNA damage in children's nasal epithelium and, further, the identification of DNA damage in nasal proliferative epithelium could be regarded as a sentinel lesion, most likely due to severe and sustained cell injury.