Adducts to nuclear DNA and mitochondrial DNA as biomarkers in chemoprevention
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S De Flora1, R Balansky, L Scatolini
1Insitute of Hygiene and Preventive Medicine, University of Genoa, Italy.
Abstract:
DNA adducts are biomarkers evaluating the biologically effective dose of carcinogens, which reflects, more realistically than the external exposure dose, an enhanced risk of developing cancer. Likewise, inhibition of DNA adduct formation can be assumed as an indicator of decreased risk. Molecular dosimetry techniques can be exploited in anticarcinogenicity studies in animal models as well as in Phase II clinical chemoprevention trials. We have extensively used these end points in animal studies using individual carcinogens and complex mixtures. As assessed by 32P-postlabelling, DNA adducts were formed in the liver of rats fed a diet supplemented with 2-acetylaminofluorene. DNA adducts were detected by synchronous fluorescence spectrophotometry (SFS) in rat liver, lung, heart and testis following intratracheal (l.t) instillations of benzo[a]pyrene. The whole-body exposure of rats to mainstream cigarette smoke resulted in the appearance of DNA adducts in lung, heart, aorta and kidney, whereas adducts were not detected by SFS in liver, brain, oesophagus and testis. Moreover, typical diagonal radioactive zones and multiple DNA adducts were revealed by 32P-postlabelling in the tracheal epithelium, nasal mucosa, aorta and testis of smoke-exposed rats. Formation of adducts to lung DNA, as assessed by both 32P-postlabelling and SFS, also occurred in rats receiving i.t. instillations of air particulate extracts from polluted urban and rural areas. The oral administration of the thiol N-acetylcysteine (NAC) significantly inhibited the formation of DNA adducts in all organs of the rats exposed to the aforementioned carcinogens, which correlated with the parallel inhibition of biochemical, cytogenetic and histopathological alterations as well as with inhibition of preneoplastic and neoplastic lesions in rodents. Our working hypothesis is that DNA adducts in trachea/lung, heart and aorta may be associated with lung cancer, cardiomyopathies and atherosclerosis, respectively. DNA adducts were consistently detectable in the DNA of smooth muscle cells from abdominal aorta specimens taken at surgery from atherosclerotic patients. Even broader are the consequences of mitochondrial (mt) DNA impairment, which has been associated with aging, cancer, and other degenerative diseases. Our data show that adduct levels are consistently higher in mtDNA than in the nuclear DNA in different organs of rats exposed either to benzo[a]pyrene, 2-acetylaminofluorene or cigarette smoke. NAC significantly decreased the formation of adducts to mtDNA when administered with drinking-water. Inhibition of adducts to nuclear DNA is one of the end points evaluated in ongoing Phase II chemoprevention trials in high-risk individuals.
Insights
DNA adducts serve as biomarkers for carcinogen exposure and cancer risk. The thiol N-acetylcysteine (NAC) effectively inhibited DNA adduct formation in animal models, suggesting reduced cancer risk.
Area of Science:
- Biomarkers and Molecular Dosimetry
- Carcinogenesis and Chemoprevention Research
- Environmental Health and Toxicology
Background:
- DNA adducts are crucial biomarkers for assessing the biologically effective dose of carcinogens, offering a more realistic reflection of cancer risk than external exposure.
- Inhibition of DNA adduct formation is a key indicator of decreased cancer risk, making molecular dosimetry valuable in anticarcinogenicity studies.
- Mitochondrial DNA (mtDNA) impairment is linked to aging, cancer, and degenerative diseases, with adduct levels often higher in mtDNA than nuclear DNA.
Purpose of the Study:
- To investigate the role of DNA adducts as biomarkers of carcinogen exposure and cancer risk.
- To evaluate the chemopreventive efficacy of N-acetylcysteine (NAC) in inhibiting DNA adduct formation.
- To explore the association between DNA adducts in specific organs and associated diseases like lung cancer, cardiomyopathies, and atherosclerosis.
Main Methods:
- Utilizing 32P-postlabeling and synchronous fluorescence spectrophotometry (SFS) to detect DNA adducts in various rat organs.
- Exposing rats to carcinogens like 2-acetylaminofluorene, benzo[a]pyrene, cigarette smoke, and air particulate extracts.
- Administering N-acetylcysteine (NAC) orally or in drinking water to assess its inhibitory effects on DNA adduct formation.
Main Results:
- DNA adducts were detected in multiple organs (liver, lung, heart, aorta, kidney, testis, tracheal epithelium, nasal mucosa) following exposure to various carcinogens.
- N-acetylcysteine (NAC) significantly inhibited DNA adduct formation in all tested organs across different exposure models.
- Adduct levels were consistently higher in mitochondrial DNA (mtDNA) compared to nuclear DNA in exposed rat organs.
- DNA adducts were also detected in smooth muscle cells from the aorta of atherosclerotic patients.
Conclusions:
- DNA adducts are reliable biomarkers for evaluating carcinogen exposure and cancer risk, with potential implications for lung cancer, cardiomyopathies, and atherosclerosis.
- N-acetylcysteine (NAC) demonstrates significant chemopreventive potential by inhibiting DNA adduct formation in nuclear and mitochondrial DNA.
- The findings support the use of DNA adduct inhibition as an endpoint in chemoprevention trials for high-risk individuals.