The assessment of DNA damage and repair in rat nasal epithelial cells

A comparative study of chemically induced DNA damage in isolated nasal mucosa cells of humans and rats assessed by the alkaline comet assay

Single-cell microgel electrophoresis (comet) assay was used to study genotoxic effects in human nasal mucosa cells and rat nasal and ethmoidal mucosa cells in vitro. Human cells were obtained from tissue samples of 10 patients (3 females/7 males), who underwent surgery (conchotomy) for treatment of nasal airway obstruction. Rat nasal mucosa cells were derived from male Sprague-Dawley rats. Cells were exposed for 1 h to either N-nitrosodiethanolamine (NDELA), epichlorohydrin (EPI), 1,2-epoxybutane (EPB), ethylene dibromide (EDB), or 1,2-dibromo-3-chloropropane (DBCP). Dimethyl sulfoxide (DMSO) was used as negative control. Alkaline comet assay was performed according to a standard protocol and DNA damage was quantified as Olive tail moment using image analysis system. All test substances induced an increase in DNA damage in human and rat cells. The absolute amount of DNA damage in rat nasal mucosa cells was usually higher than in ethmoidal mucosa cells. Human nasal mucosa cells were found to be less sensitive than rat mucosa cells to the genotoxic activities of DBCP (lowest effective concentration in human cells [LEC(human)]: 1.5, in rat cells [LEC(rat)]: 0.01 mM) and NDELA (LEC(human): 25, LEC(rat): 12.5 mM), whereas EPB-treated cells were almost equal (LEC(human) and LEC(rat) 0.78 mM). NDELA induced a marked concomitant cytotoxicity. For EPI (LEC(human) and LEC(rat): 0.097 mM) and EDB (LEC(human): 0.195, LEC(rat): 0.048 mM), pronounced interindividual differences were observed in human samples.

Renal toxicity after chronic inhalation exposure of rats to trichloroethylene

Male Long-Evans rats were exposed to 0 (controls) or 500 ppm trichloroethylene (TRI) for 6 months, 6 h daily, and 5 days a week. The TRI metabolites trichloroethanol (TCE) in blood and trichloroacetic acid (TCA) in urine were measured. Specific parameters related to the renal damage were determined in urine [biomarker for glomerular damage: high molecular weight proteins (HMW), albumin (ALB); for proximal tubular damage: N-acetyl-beta-D-glucosaminidase (NAG), low-molecular-weight-proteins (LMW)]. Significantly increased concentrations of NAG and LMW in urine of exposed rats were detected. No DNA-strand breaks in kidney cells could be detected using the comet assay, and histological examinations were performed. Histological alterations were observed in glomeruli and tubuli of exposed rats. The release of biomarkers for nephrotoxicity suggested alterations preferably in the proximal tubules of the exposed rats.

Nickel subsulfide is genotoxic in vitro but shows no mutagenic potential in respiratory tract tissues of BigBlue rats and Muta Mouse mice in vivo after inhalation

Carcinogenic nickel compounds are known to induce promutagenic DNA lesions such as DNA strand breaks and DNA adducts in cultured mammalian cells. In standard mutation assays, in contrast, they were found to be either inactive or weakly active. In our in vitro mutation studies in a lacI transgenic embryonic fibroblast cell line, nickel subsulfide (Ni3S2) increased mutation frequency up to 4. 5-fold. We subsequently applied the comet assay and transgenic rodent mutation assays to investigate the DNA damaging effect and mutagenic potential of nickel subsulfide in target cells of carcinogenesis. A 2-h in vitro treatment of freshly isolated mouse nasal mucosa and lung cells with nickel subsulfide clearly induced DNA fragmentation in a concentration dependent manner. The strong effect was not seen in the same cell types following inhalative treatment of mice and rats, leading only in the mouse nasal mucosa to high DNA damage. When the same inhalative treatment was applied to lacZ and lacI transgenic mice and rats, the spontaneous mutation frequency of these target genes in the respiratory tissues was not increased. These results support a recently proposed non-genotoxic model of nickel carcinogenesis, which acts through gene silencing via DNA methylation and chromatin condensation. This model may also explain our in vitro mutation data in the lacI transgenic cell line, in which nickel subsulfide increased mutation frequency, but in about one-third of the mutants, molecular analysis did not reveal any DNA sequence change in the coding region of the lacI gene despite of the phenotypic loss of its function.

Metabolic capacity of nasal tissue interspecies comparisons of xenobiotic-metabolizing enzymes

High levels of xenobiotic-metabolizing enzymes occur in the nasal mucosa of all species studied. In certain species, including rats and rabbits, unique enzymes are present in the nasal mucosa. The function of these enzymes is not well understood, but it is thought that they play a role in protecting the lungs from toxicity of inhalants. The observation that several nasal xenobiotic-metabolizing enzymes accept odorants as substrates may indicate that these enzymes also play a role in the olfactory process. Xenobiotic-metabolizing enzymes were found in the nasal cavity around 15 years ago. Since that time, much has been learned about the nature of the enzymes and the substrates they accept. In the present review, this information is summarized with special attention to species differences in xenobiotic-metabolizing enzymes of the nasal cavity. Such differences may be important in interpreting the results of toxicity assays in animals because rodents are apparently more susceptible to nasal toxicity after exposure to inhalants than are humans.

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.

Recommended protocols based on a survey of current practice in genotoxicity testing laboratories: I. Unscheduled DNA synthesis assay in rat hepatocyte cultures

A protocol based primarily on current laboratory practices in the performance of the unscheduled DNA synthesis (UDS) assay with primary rat hepatocyte cultures has been developed. These guidelines were developed using tabulated responses to a detailed questionnaire completed by North American and European governmental, university and contract laboratories involved with the UDS test. This report identifies those modifications to previously described methodologies which are used on a regular basis and also serves to clarify confusing or inconsistent practices. Although this protocol pertains specifically to the use of primary rat hepatocyte cultures, it can be modified to incorporate other types of cells in which certain aspects remain the same.

Nasal cavity enzymes involved in xenobiotic metabolism: effects on the toxicity of inhalants

A decade ago, the ability of nasal tissues to metabolize inhalants was only dimly suspected. Since then, the metabolic capacities of nasal cavity tissues has been extensively investigated in mammals, including man. Aldehyde dehydrogenases, cytochrome P-450-dependent monooxygenases, rhodanese, glutathione transferases, epoxide hydrolases, flavin-containing monooxygenases, and carboxyl esterases have all been reported to occur in substantial amounts in the nasal cavity. The contributions of these enzyme activities to the induction of toxic effects from inhalants such as benzo-a-pyrene, acetaminophen, formaldehyde, cocaine, dimethylnitrosamine, ferrocene, and 3-trifluoromethylpyridine have been the subject of dozens of reports. In addition, the influence of these enzyme activities on olfaction and their contribution to vapor uptake is beginning to receive attention from the research community. Research in the next decade promises to provide answers to the many still unanswered questions posed by the presence of the substantial xenobiotic metabolizing capacity of the nasal cavity.

Examination of potential mechanisms of carcinogenicity of 1,4-dioxane in rat nasal epithelial cells and hepatocytes

Several long-term studies with 1,4-dioxane (dioxane) have shown it to induce liver tumors in mice, and nasal and liver tumors in rats when administered in amounts from 0.5 to 1.8% in the drinking water (Argus et al. 1965; Kociba et al. 1974; National Cancer Institute, 1978). In order to examine potential mechanisms of action, chemically-induced DNA repair (as an indicator of DNA reactivity) and cell proliferation (as an indicator of promotional activity) were examined in nasal turbinate epithelial cells and hepatocytes of male Fischer-344 rats treated with dioxane. Neither dioxane nor 1,4-dioxane-2-one, one of the proposed metabolites, exhibited activity in the in vitro primary rat hepatocyte DNA repair assay, even from cells that had been isolated from animals given either 1 or 2% dioxane in the drinking water for 1 week to induce enzymes that might be responsible for producing genotoxic metabolites. No activity was seen in the in vivo hepatocyte DNA repair assay in animals given a single dose of up to 1000 mg/kg dioxane or up to 2% dioxane in the drinking water for 1 week. Treatment of rats with 1.0% dioxane in the drinking water for 5 days yielded no increase in liver/body weight nor induction of palmitoyl CoA oxidase, indicating that dioxane does not fit into the class of peroxisomal proliferating carcinogens. The percentage of cells in DNA synthesis phase (S-phase) was determined by administration of 3H-thymidine and subsequent quantitative histoautoradiography. The hepatic labeling index (LI) did not increase at either 24 or 48 h following a single dose of 1000 mg/kg dioxane.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of unscheduled DNA synthesis in Fischer 344 rat pachytene spermatocytes exposed to caprolactam or benzoin in vivo

Male Fischer 344 rats were treated with the non-carcinogenic chemicals CAP and ZOIN. The spermatogenic cells were isolated at selected times post-exposure for assessment of chemically-induced DNA damage by quantitative autoradiography of unscheduled DNA synthesis (UDS). Neither chemical (750 mg/kg administered by gavage) induced UDS in pachytene spermatocytes isolated 12, 24 or 48 h after treatment.

Unscheduled DNA synthesis in rat tracheal epithelial cells, hepatocytes and spermatocytes following exposure to methyl chloride in vitro and in vivo

Measurement of DNA repair as unscheduled DNA synthesis (UDS) in vitro following exposure in vivo in multiple tissues from the same treated animal can provide valuable information relating to the tissue- and organ-specificity of chemically induced DNA damage. UDS was evaluated in primary cultures of rat tracheal epithelial cells, hepatocytes and pachytene spermatocytes after exposure in vitro to methyl chloride (MeCl), and after isolation from the same treated animal following inhalation exposure in vivo. Concentrations of 1-10% MeCl in vitro induced UDS in hepatocytes and spermatocytes, but not in tracheal epithelial cells. Inhalation exposure to MeCl in vivo (3000-3500 ppm 6 h/day for 5 successive days) failed to induce DNA repair in any cell type. In vivo exposure to 15 000 ppm MeCl for 3 h also failed to induce UDS in tracheal epithelial cells and spermatocytes, but did cause a marginal increase in UDS in hepatocytes. Thus, MeCl appears to be a weak, direct-acting genotoxicant. While activity could be measured in hepatocytes and spermatocytes directly in vitro, only extremely high concentrations of MeCl elicited a response in the whole animal, and then only in hepatocytes.