Mass spectrometric profiling of DNA adducts in the human stomach associated with damage from environmental factors

Abstract

Background A comprehensive understanding of DNA adducts, one of the most plausible origins of cancer mutations, is still elusive, especially in human tissues in clinical settings. Recent technological developments have facilitated the identification of multiple DNA adducts in a single experiment. Only a few attempts toward this “DNA adductome approach” in human tissues have been reported. Geospatial information on DNA adducts in human organs has been scarce. Aim Mass spectrometry of human gastric mucosal DNA was performed to identify DNA adducts associated with environmental factors. Materials and methods From 59 subjects who had received gastrectomy for gastric cancer, 306 samples of nontumor tissues and 15 samples of tumors (14 cases) were taken for DNA adductome analysis. Gastric nontumor tissue from autopsies of 7 subjects without gastric cancer (urothelial cancer, hepatocellular carcinoma, lung cancer each; the other four cases were without any cancers) was also investigated. Briefly, DNA was extracted from each sample with antioxidants, digested into nucleosides, separated by liquid chromatography, and then electrospray-ionized. Specific DNA adducts were identified by mass/charge number and column retention time compared to standards. Information on lifestyle factors such as tobacco smoking and alcohol drinking was taken from the clinical records of each subject. Results Seven DNA adducts, including modified bases, C5-methyl-2′-deoxycytidine, 2′-deoxyinosine, C5-hydroxymethyl-2′-deoxycytidine, N6-methyl-2′-deoxyadenosine, 1,N6-etheno-2′-deoxyadenosine, N6-hydroxymethyl-2′-deoxyadenosine, and C8-oxo-2′-deoxyguanosine, were identified in the human stomach and characterized. Intraindividual differences according to the multiple sites of these adducts were noted but were less substantial than interindividual differences. N6-hydroxymethyl-2′-deoxyadenosine was identified in the human stomach for the first time. The amount of C5-hydroxymethyl-2′-deoxycytidine was higher in the stomachs of subjects without gastric cancer than in the nontumor and tumor portions of the stomach in gastric cancer patients. Higher levels of 1,N6-etheno-2′-deoxyadenosine were detected in the subjects who reported both smoking and drinking than in those without these habits. These DNA adducts showed considerable correlations with each other. Conclusions We characterized 7 DNA adducts in the nontumor portion of the human stomach in both gastric cancer subjects and nongastric cancer subjects. A reduction in C5-hydroxymethyl-dC even in the nontumor mucosa of patients with gastric cancer was observed. Smoking and drinking habits significantly influenced the quantity of one of the lipid peroxidation-derived adducts, etheno-dA. A more expansive DNA adductome profile would provide a comprehensive understanding of the origin of human cancer in the future.

A DNA adductome analysis revealed a reduction in the global level of C5-hydroxymethyl-2′-deoxycytidine in the non-tumoral upper urinary tract mucosa of urothelial carcinoma patients

“…Reductions in 5hmdC levels in the non-tumoral portion of patients with malignant tumors have been reported in other diseases. We previously demonstrated that the global levels of 5hmdC were lower in the non-tumor gastric mucosa of gastric cancer patients than in control gastric mucosa [ 10 ]. Other pathological changes in non-tumoral tissue have also been detected.…”

“…DNA adducts in human tissue have been investigated as the cause of DNA mutations in the lungs and gastrointestinal tract, which are directly exposed to potential procarcinogens and mutagens derived from environmental substances, such as tobacco smoke, polluted air, alcohol, and dietary carcinogens. Thus, the DNA lesions caused by these environmental constituents have been detected in the lungs and gastrointestinal tract [ 7 – 10 ]. The urinary system, which is constantly exposed to urine containing hydrophilic phase II metabolites, is another organ that is exposed to many environmental mutagens.…”

Geospatial Assessments of DNA Adducts in the Human Stomach: A Model of Field Cancerization

“…As described above, we have reported an interindividual variance in the accumulation of DNA adducts in human gastric mucosae [57]. Although we also showed that the intraindividual difference in DNA adducts was small, we reanalyzed all the available data according to their anatomical information.…”

“…To further explore the DNA adducts observed in the human stomach, we analyzed gastric mucosae resected from gastric cancer or non-gastric cancer patients using widetargeted identification of DNA adducts by liquid chromatography coupled with mass spectrometry [57]. We identified seven DNA adducts including modified bases, C5-methyl-2 -deoxycytidine, 2 -deoxyinosine, C5-hydroxymethyl-2 -deoxycytidine, N6-methyl-2deoxyadenosine, 1,N6-etheno-2 -deoxyadenosine, N6-hydroxymethyl-2 -deoxyadenosine, and C8-oxo-2 -deoxyguanosine, in the human stomach.…”

Current and Future Methodology for Quantitation and Site-specific Mapping the Location of DNA Adducts

“…For example, applying a nontargeted 'omics' approach, thousands of potential DNA adduct m/z features were observed in human tissues such as lung, bronchia or saliva [86][87][88]. A challenging task will be to accurately identify the low abundant DNA adducts resulting from exogenous sources that are dwarfed by epigenic marks and endogenous DNA adducts, that are present at levels several orders of magnitude higher [89,90].…”