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Metabolic activation of 1-nitropyrene to a mammalian cell mutagen and a carcinogen
F A Beland1, B A Smith, J R Thornton-Manning
1National Center for Toxicological Research, Jefferson, AR 72079.
Abstract:
1. The mutagenicity of 1-nitropyrene metabolites in Chinese hamster ovary (CHO) cells, in the absence of rat liver S9, decreased in the order 6-hydroxy-1-nitropyrene > 1-nitropyrene 9,10-oxide > 1-nitropyrene 4,5-oxide approximately 3-hydroxy-1-nitropyrene approximately 8-hydroxy-1-nitropyrene > 1-nitropyrene. The order of mutagenicity with rat liver S9 was 1-nitropyrene 4,5-oxide approximately 6-hydroxy-1-nitropyrene approximately 1-nitropyrene 9,10-oxide > 3-hydroxy-1-nitropyrene approximately 1-nitropyrene > 8-hydroxy-1-nitropyrene. 2. 1-Nitropyrene 4,5-oxide reacted with calf thymus DNA to give one or several closely related adducts. The same adducts were detected in CHO cells incubated with 1-nitropyrene 4,5-oxide. Inclusion of a nitroreductase, xanthine oxidase, in the incubations with calf thymus DNA resulted in the formation of an additional adduct identified as N-(deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP). 3. 1-Nitropyrene 9,10-oxide reacted with calf thymus DNA to give an adduct pattern similar to that observed with 1-nitropyrene 4,5-oxide. Incubation of 1-nitropyrene 9,10-oxide with CHO cells resulted in the formation of the same adducts along with dG-C8-AP. 4. dG-C8-AP and N-(deoxyguanosin-8-yl)-1-amino-x-nitropyrene (x = 3, 6 or 8; dG-C8-ANP) were detected in injection site DNA from Sprague-Dawley rats treated with 1-nitropyrene. In mammary gland DNA, dG-C8-AP and an unidentified adduct were found. dG-C8-ANP was the only DNA adduct detected in the livers of newborn CD-1 mice and the lungs of A/J mice dosed with 1-nitropyrene.
Insights
The mutagenicity of 1-nitropyrene metabolites varies, with hydroxylated forms and epoxides showing higher activity in Chinese hamster ovary (CHO) cells. DNA adducts, including N-(deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP), are formed in vivo and in vitro.
Area of Science:
- Environmental Chemistry
- Toxicology
- Molecular Biology
Background:
- 1-Nitropyrene is a polycyclic aromatic hydrocarbon found in environmental pollutants.
- Metabolites of 1-nitropyrene can be mutagenic and form DNA adducts.
- Understanding the mutagenicity and DNA adduct formation is crucial for risk assessment.
Purpose of the Study:
- To investigate the mutagenicity of various 1-nitropyrene metabolites in Chinese hamster ovary (CHO) cells.
- To identify and characterize DNA adducts formed by 1-nitropyrene metabolites in vitro and in vivo.
Main Methods:
- Mutagenicity assays were performed in CHO cells with and without rat liver S9 activation.
- DNA adducts were analyzed using calf thymus DNA and cell cultures incubated with 1-nitropyrene metabolites.
- Adducts were also detected in DNA from Sprague-Dawley rats, CD-1 mice, and A/J mice treated with 1-nitropyrene.
Main Results:
- Mutagenicity order varied with and without S9 activation, with 6-hydroxy-1-nitropyrene and epoxides showing significant activity.
- 1-Nitropyrene 4,5-oxide and 9,10-oxide formed similar DNA adducts in calf thymus DNA and CHO cells.
- N-(deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP) and N-(deoxyguanosin-8-yl)-1-amino-x-nitropyrene (dG-C8-ANP) were identified in vivo.
Conclusions:
- The mutagenicity of 1-nitropyrene metabolites is dependent on metabolic activation.
- Specific DNA adducts, dG-C8-AP and dG-C8-ANP, are formed from 1-nitropyrene exposure in various species.
- These findings contribute to understanding the genotoxic mechanisms of 1-nitropyrene.