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

https://doi.org/10.1016/S0891-5849(99)00156-2Get rights and content

Abstract

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 μm. 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.

Introduction

It has been reported by many investigators that cellular DNA damage occurrs due to oxygen free radicals generated in ionizing radiation, environmental mutagens and carcinogens, and may be involved in mutagenesis, carcinogenesis and the aging process [1], [2], [3]. The C-8 position of deoxyguanosine residue in DNA produces 8-hydroxyguanosine (8-OHdG), one of the most critical lesions generated from deoxyguanosine in DNA by oxygen radicals [4], [5], [6]. Determination of 8-OHdG in humans has been investigated by many researchers, in studies on polymorphonuclear leukocytes [7], peripheral lymphocytes [8], peripheral lung tissues [9], and breast tissues with breast cancer [10]. However, it has also been reported that fullerene C60, as carbon vapor produced by laser irradiation of graphite, also generated singlet oxigen, and 8-OHdG was formed in an in vitro system by lipid peroxidation [11].

Diesel exhaust particles were mutagenic for Salmonella typhimurium and mammalian cell cultures, and carcinogenic in animal experiments [12]. In addition to cigarette smoke, the large increase in lung cancer incidence was thought to involve diesel exhaust particles, and it has been reported that a significant correlation between air pollution and lung cancer was epidemiologically observed [13]. Major mutagenic and carcinogenic components in the particles have been demonstrated on the basis of analysis of their biological and chemical properties [12]. In these components, nitrated polycyclic aromatic compounds (NO2-PAH), substantial mutagens and carcinogens were deposited in human lung tissues by inhaling environmental air pollutants even if the deposited amounts of each compound were at low levels [14], [15]. 8-OHdG formation causing oxidative damage has already been reported as causing pulmonary injury due to diesel exhaust particles (DEPs) [16], and motorcycle exhaust particles [17], and the DEP toxicity was found to be due to production of superoxide (O2•−) and a hyroxyl radical (•OH).

The present study aimed to evaluate 8-OHdG detected by administration of DEPs in mice, and moreover, to demonstrate whether or not carboneceous particles in diesel exhaust particles may be involved in the process of oxidative damage in test done in vivo using mice.

Section snippets

Chemicals

1-Nitropyrene (1-NP) and 1,8-dinitropyrene (1,8-DNP) were prepared as described previously [14], and benzo[a]pyrene (B[a]P) was purchased from Aldrich (Milwaukee, WI, USA). Catalase, super oxide dismutase (SOD), and deferoxamine mesylate were obtained from Sigma Chemical Co. (St Louis, MO, USA).

Lung specimens

Lung specimens with carcinoma (80 cases) were surgically resected as reported previously [14], and bioassayed for mutagenicity. The ages of the patients ranged from 10 to 85 years. Lung specimens

Mutagenicity of extracts of lung tissues for salmonella strain YG3003

Lung tissues (81 cases) resected from patients with carcinoma were treated with β-glucuronidase, and extracted with dichloromethane as described in Materials and Methods. Mutagenic activity of the lung tissue extracts indicated an increase with age, though it was not statistically significant (Fig. 1). The strain YG3003 used in this study was a mutant that was sensitive to active oxygen. Therefore, it was suggested that the extracts from lung tissue induced oxidative damage in the DNA residue

Discussion

It has been suggested that DEPs may be associated with human lung carcinogenesis. The extracts of DEPs were obviously mutagenic for Salmonella strains and mammalian cell cultures, and also carcinogenic in rats and mice [12]. These mutagenic and carcinogenic agents were mostly composed of various chemicals such as polycyclic aromatic hydrocarbons and their nitrated derivatives. Similarly, the extracts from DEPs were found to be mutagenic for Salmonella strains YG3003 originating from TA102, a

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