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DNA adducts: endogenous and induced
1School of Epidemiology and Health Sciences, University of Manchester, United Kingdom.
Abstract:
Human exposure to DNA damaging agents can arise from exogenous sources or endogenous processes that occur normally or in pathological states. DNA isolated from human tissues, obtained from the very young to the old, contains detectable amounts of a number of different types of DNA adducts that reflect exposure to both known carcinogens and as yet unidentified genotoxic agents. The levels of DNA damage observed in human studies as a result of exogenous exposures (noniatrogenic) is of the order of 1 adduct per 10(7)-10(9) normal DNA bases, whereas that arising from endogenous exposures may potentially be several orders of magnitude higher. Large interindividual variations in DNA adduct levels have been reported, and these are probably the result of host and environmental factors, although variation in analytical and sampling procedures may also play a role. It is important to recognize that the presence of DNA adducts in a tissue does not necessarily indicate a specific tumorigenic risk for that tissue, as other factors downstream of DNA adduct formation (including DNA repair and cell proliferation) play an important role in determining overall risk.
Insights
Human DNA contains adducts from environmental and internal exposures, with internal sources potentially causing higher damage. Individual variations in DNA adduct levels are significant, influenced by various factors.
Area of Science:
- Environmental Health
- Toxicology
- Molecular Biology
Background:
- Human DNA adducts indicate exposure to genotoxic agents from external and internal sources.
- DNA damage levels vary, with endogenous exposures potentially causing significantly higher adduct levels than exogenous ones.
- Significant interindividual variability in DNA adduct levels exists, influenced by host, environmental, and analytical factors.
Purpose of the Study:
- To investigate the presence and levels of DNA adducts in human tissues.
- To understand the sources and variability of DNA damage in humans.
- To contextualize DNA adducts within the broader framework of tumorigenic risk.
Main Methods:
- Analysis of DNA adducts in human tissues across different age groups.
- Quantification of DNA damage from exogenous (non-iatrogenic) and endogenous exposures.
- Assessment of interindividual variations in DNA adduct levels.
Main Results:
- Detectable levels of various DNA adducts found in human DNA from all age groups.
- Exogenous DNA damage is approximately 1 adduct per 10(7)-10(9) bases.
- Endogenous exposures may lead to DNA damage levels several orders of magnitude higher than exogenous exposures.
- Significant interindividual variations in DNA adduct levels were observed.
Conclusions:
- Human DNA adducts are biomarkers of exposure to genotoxic agents.
- Both exogenous and endogenous factors contribute to DNA damage in humans.
- DNA adduct levels alone do not determine tumorigenic risk; DNA repair and cell proliferation are critical.
- Further research is needed to identify unknown genotoxic agents and understand risk factors.