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Free radicals in arylamine carcinogenesis
National Cancer Institute Monograph
|December 1, 1981
Summary
Free radicals are implicated in cancer. This study shows heme compounds catalyze N-hydroxy-2-fluorenylacetamide oxidation, forming a nitroxyl free radical intermediate that binds to lipids, creating a 2-nitroso-fluorene lipid adduct.
Area of Science:
- Biochemistry
- Carcinogenesis Research
- Free Radical Chemistry
Background:
- The role of free radicals in cancer development is under active investigation.
- N-hydroxy-2-fluorenylacetamide (N-OH-2-FAA) is a compound of interest in carcinogenicity studies.
- Heme compounds and hydroperoxides can catalyze oxidative reactions.
Purpose of the Study:
- To investigate the formation of free radical intermediates during N-OH-2-FAA oxidation.
- To identify the role of lipid hydroperoxides and cytochrome P420 in this process.
- To characterize the formation and properties of 2-nitroso-fluorene lipid adducts (N-O-LAF).
Main Methods:
- In vitro oxidation assays using heme compounds and hydroperoxides.
- Investigation of reaction kinetics with different cytochrome P420 spin states.
- Analysis of N-O-LAF formation in rat liver microsomes and its interaction with membrane lipids.
- Mutagenicity testing of 2-nitrosofluorene (2-NF) in Salmonella typhimurium.
Main Results:
- Heme compounds catalyzed N-OH-2-FAA oxidation to a nitroxyl free radical, forming 2-NF and N-acetoxy-2-fluorenylacetamide (N-AcO-2-FAA).
- Lipid hydroperoxides were effective substrates, particularly in rat mammary gland cells.
- High-spin cytochrome P420 catalyzed the reaction, while low-spin forms were ineffective.
- 2-NF formed covalent adducts (N-O-LAF) with unsaturated membrane lipids, existing as nitroxyl free radicals.
- N-O-LAF formation was observed in rat liver microsomes and inhibited by paraoxon.
- Mutagenicity of 2-NF was enhanced in bacteria with higher unsaturated membrane lipid content, though synthesized adducts showed low mutagenicity.
Conclusions:
- Free radical intermediates are formed during N-OH-2-FAA metabolism, potentially contributing to carcinogenesis.
- The formation of 2-nitroso-fluorene lipid adducts (N-O-LAF) represents a novel mechanism of chemical interaction with cell membranes.
- The reactivity and mutagenicity of these adducts warrant further investigation in the context of cancer risk.