Abstract
The measurement of DNA adducts provides important information about human exposure to genotoxic chemicals and can be employed to elucidate mechanisms of DNA damage and repair. DNA adducts can serve as biomarkers for interspecies comparisons of the biologically effective dose of procarcinogens and permit extrapolation of genotoxicity data from animal studies for human risk assessment. One major challenge in DNA adduct biomarker research is the paucity of fresh frozen biopsy samples available for study. However, archived formalin-fixed paraffin-embedded (FFPE) tissues with clinical diagnosis of disease are often available. We have established robust methods to recover DNA free of crosslinks from FFPE tissues under mild conditions which permit quantitative measurements of DNA adducts by liquid chromatography-mass spectrometry. The technology is versatile and can be employed to screen for DNA adducts formed with a wide range of environmental and dietary carcinogens, some of which were retrieved from section-cuts of FFPE blocks stored at ambient temperature for up to nine years. The ability to retrospectively analyze FFPE tissues for DNA adducts for which there is clinical diagnosis of disease opens a previously untapped source of biospecimens for molecular epidemiology studies that seek to assess the causal role of environmental chemicals in cancer etiology.
Highlights
The measurement of DNA adducts provides important information about human exposure to genotoxic chemicals and can be employed to elucidate mechanisms of DNA damage and repair
Our findings demonstrate that the DNA can be recovered from formalin-fixed paraffin-embedded (FFPE) tissue to analyze DNA adducts of aristolochic acid I (AA-I) in FFPE tissue, and adducts of AA-I or other carcinogens may be correlated with mutational signatures induced in tumor tissue
We examined DNA adducts of four important classes of environmental and dietary carcinogens: polycyclic aromatic hydrocarbons (PAHs) (B[a]P), aromatic amines (4-ABP), HAAs (PhIP), and N-nitroso compounds 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is found in tobacco and a lung carcinogen [21,107]
Summary
Humans are continuously exposed to potentially hazardous chemicals in the environment, diet, medicines, and through occupational exposures Many of these chemicals undergo biotransformation by phase I and/or phase II enzymes to produce reactive electrophiles that can form adducts with macromolecules [1]. The second pathway involves aryl-oxidation of one of the phenyl rings to yield 4-hydroxytamoxifen quinone methide, a reactive electrophile that can form the DNA adducts. Both pathways lead to (Z)- or (E)-dG-N2 -4-hydroxytamoxifen. The metabolism of carcinogens and their biological effects in animal models can differ from humans because of species differences in catalytic activities of phase I and II enzymes involved in bioactivation or detoxification [10,16,17,18]. Life-style factors such as tobacco smoking, diet, and environmental pollution often represent long-term exposures, and current adduct levels of carcinogens from these exposures are likely to correlate with adduct levels that existed during the time of tumor initiation and progression
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