O6-methylguanine-DNA methyltransferase activity in tissues and cells of the rat respiratory tract

DNA damage in the nasal passageway: a literature review

The purpose of this review is to provide a compilation of work examining DNA damage in the nasal cavity. There are numerous methods to identify and quantify damage to DNA and the diversity of methods and toxicologic endpoints is illustrated by the range of studies presented here. There are a large number of independent studies measuring endpoints in the upper respiratory tract; however, with regard to toxicant induced DNA damage in the nasal passageway, the effects of two compounds, 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and formaldehyde (HCHO), appear to have been extensively characterized. The body of work on NNK and formaldehyde have provided insights into molecular mechanisms of DNA damage and repair and induced cell replication and its relationship to nasal cancer. With new technologies and molecular techniques, the sensitivity to enable evaluations of the minute quantities of nasal tissue available in test species and human biopsy impact the study of the nasal-toxicant interactions. As methods used to characterize DNA damage increase in sensitivity, the importance of both exogenous and endogenous sources of DNA damage, steady-state levels of cellular damage, repair, and resulting mutations, low-dose exposure assessments and inter-species extrapolation will become increasingly complex. Additional studies of DNA damage in the nasal passage will undoubtedly challenge future estimations of risk and impact what are perceived to be acceptable levels of exposure to known and predicted carcinogens. The aim of this paper is to provide to the interested scientist literature relevant to the effects of agents on nasal DNA, so that areas of insufficient information can be identified and used to further develop and expand the knowledge base for nasal DNA toxicant interactions.

Metabolism and elimination of inhaled drugs and airborne chemicals from the lungs

Inhalation is a common route by which people are exposed to many toxic chemicals. Inhaled chemicals can deposit in various regions of the respiratory tract. The factors that determine deposition site include chemical reactivity and water solubility for gases and vapors, and shape, physical size, and density for particles. Metabolic activation of chemicals by respiratory tract tissues may play an important role in both the pathogenesis of diseases in these tissues or in modifying the effective dose to tissues distal to the respiratory tract. This paper is a review of the state-of-the-knowledge regarding the regional distribution of xenobiotic metabolizing enzymes in the conducting airways and pulmonary tissue of several animal species, including humans. All segments of the respiratory tract, including the periphery of the pulmonary compartment, contain enzymes (Phase I and II) that metabolize xenobiotic compounds. In general, the data indicate that the pulmonary tissue has a higher metabolic activity toward inhaled chemicals than other regions of the respiratory tract, such as the trachea and bronchi. However, even within an anatomical region of the respiratory tract, there is a non-uniform distribution of enzymes within the individual cell types. Significant species differences exist in metabolic activity toward a number of substrates. However, some generalities can be made. Firstly, the ratio of activating/inactivating enzyme activities in all species is, in general, less than 1. A second point is that this ratio is considerably higher in rodent animal species than humans. This indicates that caution needs to be exercised when extrapolating metabolic data derived from rodents to human metabolic capability.

Immunocytochemical analysis of in vivo DNA modification

In the past decades a large number of DNA adducts induced in the intact animal by alkylating agents have been identified. The formation and repair of these adducts are important determinants, not only of mutagenesis, tumor initiation and DNA-mediated toxicity but probably also of tumor progression. Most studies on in vivo DNA modification have been performed on isolated bulk DNA. More recently, methods have been developed to study the distribution of DNA adducts at the level of either the individual gene or the individual cell. This paper reviews immunocytochemical methods to study the formation and repair of DNA adducts and other DNA modifications at the level of the individual cell. DNA modifications induced by alkylating agents and a variety of other agents including ultraviolet radiation, aromatic amines, polycyclic aromatic hydrocarbons and platinum anti-cancer drugs will be discussed. Up to now, immunocytochemical analysis of in vivo modified DNA has largely concentrated on experimental animals. These studies have revealed striking heterogeneities with regard to formation and/or repair of DNA adducts in tissues from rat, hamster and mouse. Immunocytochemical adduct analysis can be used to identify in a convenient, fast and detailed way cell types, cell stages and sites in which biological effects of the adducts might be expressed. More recently, immunocytochemical analysis of DNA adducts also proved to be feasible on in situ exposed human samples. A number of existing and potential applications in the field of chemical carcinogenesis, experimental chemotherapy and molecular epidemiology are discussed.