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Binding and repair of 2-acetylaminofluorene adducts in distinct liver cell populations
Abstract:
The study of the binding of the liver carcinogen, N-acetyl-2-aminofluorene, to the DNA of the target organ-as the probable initial step in the process of carcinogenesis-has shown that three modes of interaction occur. N-Acetyl-2-aminofluorene is covalently bound with the nitrogen to the carbon 8 of guanine (I) and with the 3-position to the free NH(2)-group of guanine (II). The third mode of interaction is formed by a covalent bond between the nitrogen of 2-aminofluorene and the carbon 8 of guanine (III). In this study the different modes of interaction were measured separately in stromal and parenchymal cells of the rat liver, after a single intraperitoneal dose. The DNA was isolated from nuclei that had been separated by 1g sedimentation. In parenchymal DNA the types of interaction I and III occur in the same amounts one day after application. In stromal cells the amount of interaction I is relatively small and interaction III predominates (ratio III:I = 5). The amount of interaction III in tetraploid hepatocytes (the largest cell population in the studied rats) per mg DNA is about two times higher than in the stromal cells. While the removal of the total amount of DNA-bound carcinogen takes place at the same rate in the two cell types, a difference in rate and efficiency of repair is observed for the different types of interaction. In tetraploid hepatocytes, interaction I is almost completely removed from the DNA 2 weeks after application, while interaction III diminishes to about 1/3 during the first week but the remaining part disappears very slowly. As shown in earlier studies, interaction II remains in the DNA at a constant level.
Insights
Liver carcinogen N-acetyl-2-aminofluorene binds DNA via three modes. Different cell types show varying binding and repair rates, impacting carcinogenesis risk.
Area of Science:
- Molecular toxicology
- Carcinogenesis research
- DNA damage and repair
Background:
- N-acetyl-2-aminofluorene is a known liver carcinogen.
- Carcinogenesis is often initiated by carcinogen-DNA binding.
- Understanding carcinogen-DNA interactions is crucial for risk assessment.
Purpose of the Study:
- To investigate the distinct binding modes of N-acetyl-2-aminofluorene to rat liver DNA.
- To compare these interactions in different liver cell types (stromal vs. parenchymal).
- To analyze the DNA repair kinetics for each binding mode in vivo.
Main Methods:
- Administration of N-acetyl-2-aminofluorene to rats via intraperitoneal injection.
- Isolation of DNA from separated stromal and parenchymal liver cells.
- Quantification of three specific N-acetyl-2-aminofluorene-DNA adducts (I, II, and III).
Main Results:
- Two binding modes (I and III) were found in equal amounts in parenchymal cells; mode III predominated in stromal cells.
- Tetraploid hepatocytes showed higher levels of interaction III compared to stromal cells.
- While total carcinogen removal rates were similar, repair efficiency differed, with mode I repaired faster than mode III.
Conclusions:
- Differential binding and repair of N-acetyl-2-aminofluorene adducts in rat liver cells suggest cell-type-specific susceptibility.
- The persistence of specific adducts, particularly mode III in hepatocytes, may be a critical factor in liver carcinogenesis.
- Further research into repair mechanisms for different adduct types is warranted.