Development of an isotope dilution liquid chromatography/tandem mass spectrometry detection method for DNA adducts of selected aromatic amines

Molecular Modeling Study of the Genotoxicity of the Sudan I and Sudan II Azo Dyes and Their Metabolites

Azo dyes are defined by the presence of a characteristic N=N group. Sudan I and Sudan II are synthetic azo dyes that have been used as coloring agents. Although animal toxicity studies suggest that Sudan dyes are mutagenic, their molecular mechanism of action is unknown, thus making it challenging to establish thresholds for tolerable daily intake or to understand how these molecules could be modified to ameliorate toxicity. In addition, dye metabolites, such as azobiphenyl and 4-aminobiphenyl, have been correlated with epigenetic alterations. We shed some light on the mechanisms of Sudan dye genotoxicity through a molecular modeling study of Sudan I and Sudan II dyes and two common metabolites interacting with DNA as adducts. The results suggest that all four adducts cause significant perturbations to the DNA helical conformation and structure; thus, it can be inferred that DNA repair and replication processes would be significantly impacted.

Profiles of primary aromatic amines, nicotine, and cotinine in indoor dust and associated human exposure in China

Despite the widespread use of primary aromatic amines (AAs) in consumer products, little is known about their prevalence in house dust. In this study, we investigated the occurrence of 35 AAs and two tobacco chemical markers (nicotine and its breakdown product cotinine) in 119 samples of house dust collected from five provinces in China. Ten of the 35 AAs and [nicotine and cotinine] were found in >80% and 100% of the samples, respectively, at concentration ranges of 29.1-19,200 (median: 700 ng/g) and 23.2-22,400 (4600) ng/g, respectively. Aniline was the predominant AA found in all dust samples (median: 257 ng/g). Dust samples from Henan and Shanxi provinces contained higher summed concentrations of the 10 AAs than those from Sichuan and Shandong, although the concentrations did not vary significantly among the five provinces (p > 0.05). A significant (p = 0.048), positive correlation (r = 0.882) existed between concentrations of nicotine and cotinine in dust samples. Similarly, concentrations of AAs were significantly correlated with those of nicotine in dust samples. Dyestuffs, rubber products, polyurethane foam and tobacco smoke are the major sources of AAs in the indoor environment. The estimated daily intakes (EDI) through dust ingestion ranged from 0.349 (adults) to 6.62 ng/kg-bw/day (toddlers) for AAs and from 1.27 to 51.1 ng/kg-bw/day for nicotine which are well below the current tolerable daily intakes.

Quantitation of DNA adducts by stable isotope dilution mass spectrometry

Exposure to endogenous and exogenous chemicals can lead to the formation of structurally modified DNA bases (DNA adducts). If not repaired, these nucleobase lesions can cause polymerase errors during DNA replication, leading to heritable mutations and potentially contributing to the development of cancer. Because of their critical role in cancer initiation, DNA adducts represent mechanism-based biomarkers of carcinogen exposure, and their quantitation is particularly useful for cancer risk assessment. DNA adducts are also valuable in mechanistic studies linking tumorigenic effects of environmental and industrial carcinogens to specific electrophilic species generated from their metabolism. While multiple experimental methodologies have been developed for DNA adduct analysis in biological samples, including immunoassay, HPLC, and ³²P-postlabeling, isotope dilution high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) generally has superior selectivity, sensitivity, accuracy, and reproducibility. As typical DNA adduct concentrations in biological samples are between 0.01-10 adducts per 10⁸ normal nucleotides, ultrasensitive HPLC-ESI-MS/MS methodologies are required for their analysis. Recent developments in analytical separations and biological mass spectrometry, especially nanoflow HPLC, nanospray ionization MS, chip-MS, and high resolution MS, have pushed the limits of analytical HPLC-ESI-MS/MS methodologies for DNA adducts, allowing researchers to accurately measure their concentrations in biological samples from patients treated with DNA alkylating drugs and in populations exposed to carcinogens from urban air, drinking water, cooked food, alcohol, and cigarette smoke.

Dietary Exposure to 2-Aminoanthracene Induces Morphological and Immunocytochemical Changes in Pancreatic Tissues of Fisher-344 Rats

Toxic chemicals ingested as the result of environmental exposures or other risk factors such as cigarette smoking may increase the risk of developing cancer and other diseases such as diabetes. 2-Aminoanthracene (2-AA) was investigated to determine toxic effects of chronic dietary exposure upon major organ systems including the pancreas. Fisher-344 rats were fed 2-AA (50-100 mg/kg of diet) and euthanized at 14, 30, 63, and 80 days. Growth, tissue histological, immunocytochemical, and clinical pathological end points were examined at each time point. Significantly elevated plasma glucose and glycated hemoglobins and reduced serum protein levels were recognized after 80 days of feeding (100 mg/kg of diet 2-AA group). Similar results were observed in rats exposed to 75 mg/kg of diet but appeared to be absent in the 50-mg/kg group. An unexpected pattern of responses suggestive of diabetic sequelae was observed in a glucose tolerance test conducted during the seventh week. After 63 and 80 days, large cytoplasmic vacuoles in islet cells were observed by light microscopy. In addition, the immunocytochemical study demonstrated beta cell insulin insufficiency at 63 and 80 days. No inflammatory infiltration of the islets was observed. These findings suggest that depletion of secretory granules occurred in the beta cells. Necrotic changes occurred in the acinar cells of the pancreas with increasing duration and dose of 2-AA. The cytological, immunocytochemical, and histological results demonstrate that chronic dietary exposure to 2-amino anthracene alters the endocrine and exocrine pancreas cellular morphology and induces diabetic-like symptoms in the Fisher-344 rat.

Liquid chromatography-electrospray ionization-mass spectrometry: the future of DNA adduct detection

Over the past 40 years considerable emphasis has been placed on the development of accurate and sensitive methods for the detection and quantitation of DNA adducts. The formation of DNA adducts resulting from the covalent interaction of genotoxic carcinogens with DNA, derived from exogenous and endogenous sources, either directly or following metabolic activation, can if not repaired lead to mutations in critical genes such as those involved in the regulation of cellular growth and subsequent development of cancer. The major analytical challenge has been to detect levels of DNA adducts at the level of 0.1-1 adducts per 10(8) unmodified DNA bases using only low microgram amounts of DNA, and with high specificity and accuracy, in humans exposed to genotoxic carcinogens derived from occupational, environmental, dietary and life-style sources. In this review we will highlight the merits as well as discuss the progress made by liquid chromatography coupled to electrospray ionization mass spectrometry as a method for DNA adduct detection.

Development of a quantitative liquid chromatography/electrospray mass spectrometric assay for a mutagenic tobacco specific nitrosamine-derived DNA adduct, O6-[4-Oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine

Liquid chromatography with electrospray tandem mass spectrometry (LC/ESI-MS/MS) was employed to quantify O6-[4-oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine (O6-pobdG), a mutagenic adduct formed by pyridyloxobutylating nitrosamines. Selected reaction monitoring (SRM) of the neutral loss of the sugar from protonated molecules of the adduct, [M + H - 116]+, was utilized for detection of O6-pobdG in pyridyloxobutylated DNA from both in vitro and in vivo sources. Quantitation was based on isotope dilution with synthetic O6-[1,2,2-2H3-4-oxo-4-(3-pyridyl)butyl]-2'-deoxyguanosine. The detection limits in this study were less than 5 fmol of pure standard and 50 fmol in 1.5 mg of DNA. This method was validated by comparing adduct levels measured with the LC/ESI-MS/MS method to those obtained with radiochemical methods in DNA alkylated with the model pyridyloxobutylating agent, [5-3H]4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone ([5-3H]NNKOAc). The pyridyloxobutyl 2'-deoxyguanosine adduct coeluting with the deuterated standard disappeared when NNKOAc-treated DNA had been reacted with the repair protein, O6-alkylguanine-DNA alkyltransferase. This result confirms that the coeluting peak is solely O6-pobdG. Preliminary studies with liver DNA isolated from NNKOAc-treated mice demonstrated that this method can be used to quantify O6-pobG in DNA from in vivo sources. The improved sensitivity and specificity of adduct detection afforded by this LC/ESI-MS/MS method will allow us to explore the role of O6-pobdG in the toxicological properties of pyridyloxobutylating nitrosamines.