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Published on: May 29, 2019
High-Resolution Mass Spectrometric Analysis of Selected DNA Adducts in Smokeless Tobacco Users' Oral Cells
Guang Cheng1, Irina Stepanov1, Dorothy K Hatsukami1
1Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota55455, United States.
Abstract:
Smokeless tobacco, used by more than 360 million people worldwide, is an accepted cause of cancers of the oral cavity, esophagus, and pancreas. DNA adducts are considered as critical intermediates in the carcinogenic process, but there are no published studies that have used structure-specific methods to identify and quantify oral cell DNA adducts in people who use smokeless tobacco. In the study presented here, we used liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry to identify and quantify DNA adducts in oral cells of 24 individuals who use smokeless tobacco and 25 individuals not using any tobacco or nicotine product. We quantified the following DNA adducts: (8R/S)-3-(2'-deoxyribos-1'-yl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purine-10(3H)-one (γ-OH-Acr-dGuo) from acrolein; (6S,8S and 6R,8R)-3-(2'-deoxyribos-1'-yl)-5,6,7,8-tetrahydro-8-hydroxy-6-methylpyrimido[1,2-a]purine-10(3H)-one [(S,R)γ-OH-Cro-dGuo] from crotonaldehyde and/or acetaldehyde; 3-methyladenine (3-Me-Ade); 7-ethylguanine (7-Et-Gua); and 8-oxo-deoxyguanosine (8-oxo-dGuo). Levels [median (min, max)] fmol/μmol dGuo or Gua, in samples in which analytes were detected, were: γ-OH-Acr-dGuo [350 (169, 2217) vs 114 (14, 278)], (6S,8S and 6R,8R)γ-OH-Cro-dGuo [1058 (222, 2569) vs not detected], and 7-Et-Gua [2445 (1052, 5389) vs 102 (13, 627)], which were significantly greater in the oral cell DNA of individuals who use smokeless tobacco than in those not using any tobacco or nicotine product (all adjusted Ps < 0.01), while amounts of 3-Me-Ade [3739 (93, 11495) vs 1447 (318, 3596) fmol/μmol Gua, adjusted P = 0.052] and 8-oxo-dGuo [1520 (513, 5232) vs 2092 (433, 3325) pmol/μmol dGuo, adjusted P = 0.13] were not significantly different between the two groups. The sizable and significant elevations of 7-Et-Gua and (6S,8S and 6R,8R)γ-OH-Cro-dGuo in oral cell DNA when smokeless tobacco was used versus controls were particularly notable and unexpected. The results of this study provide some potentially important new data regarding DNA adduct levels in oral cells of people who use smokeless tobacco.
Insights
Smokeless tobacco use significantly increases DNA adducts like 7-ethylguanine and γ-OH-Cro-dGuo in oral cells. This study identifies and quantifies these harmful adducts, providing new insights into smokeless tobacco
Area of Science:
- Toxicology
- Cancer Research
- Analytical Chemistry
Background:
- Smokeless tobacco is a known carcinogen, linked to oral, esophageal, and pancreatic cancers.
- DNA adducts are key intermediates in carcinogenesis, but oral adducts in smokeless tobacco users remain understudied.
- Structure-specific methods are crucial for accurate identification and quantification of DNA adducts.
Purpose of the Study:
- To identify and quantify specific DNA adducts in oral cells of smokeless tobacco users and non-users.
- To investigate the association between smokeless tobacco consumption and the levels of DNA adducts.
- To provide novel data on oral DNA adducts in relation to smokeless tobacco use.
Main Methods:
- Employed liquid chromatography-nanoelectrospray ionization-high resolution tandem mass spectrometry (LC-nESI-HR-MS/MS).
- Analyzed oral cells from 24 smokeless tobacco users and 25 non-users.
- Quantified DNA adducts including γ-OH-Acr-dGuo, (S,R)γ-OH-Cro-dGuo, 3-Me-Ade, 7-Et-Gua, and 8-oxo-dGuo.
Main Results:
- Significantly elevated levels of γ-OH-Acr-dGuo, (S,R)γ-OH-Cro-dGuo, and 7-Et-Gua were observed in oral cell DNA of smokeless tobacco users compared to controls (adjusted P < 0.01).
- Unexpectedly large increases in 7-ethylguanine and (6S,8S and 6R,8R)γ-OH-Cro-dGuo were noted.
- Levels of 3-methyladenine and 8-oxo-deoxyguanosine did not differ significantly between the groups.
Conclusions:
- Smokeless tobacco use is associated with significantly higher levels of specific DNA adducts in oral cells.
- The findings highlight 7-ethylguanine and (6S,8S and 6R,8R)γ-OH-Cro-dGuo as potentially important biomarkers.
- This study contributes significant new data on DNA adduct profiles in oral cells of smokeless tobacco consumers.
