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Beta-oxidized N-nitrosoalkylcarbamates as models for DNA alkylation by N-nitrosobis(2-oxopropyl)amine in Syrian
D L Nagel1, R Lewis, M Fischer
1Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha, Nebraska.
Abstract:
A single dose of N-nitrosobis(2-oxopropyl)amine (NDOPA) can selectively induce pancreatic-duct adenocarcinomas in Syrian hamsters. Multiple doses or a higher single dose can induce tumours of the liver and other organs. Our earlier studies employing NDOPA systematically labelled with 14C in the three-carbon chain showed that hamster pancreatic DNA is almost exclusively methylated and that the sole source of the methyl group is the alpha carbon of NDOPA. Hamster liver DNA was equally methylated and alkylated by a three-carbon chain. Current studies using generally labelled tritiated NDOPA with a very high specific activity have shown that the three-carbon alkylation is 2-hydroxypropylation. We have identified two adducts isolated from hamster liver DNA, N7-(2-hydroxypropyl)-guanine and O6-(2-hydroxypropyl)guanine, which contain this group, and we have also isolated and identified N7-methylguanine and O6-methylguanine in DNA from hamster liver and pancreas. beta-Oxidized N-nitrosocarbamates, ethyl N-nitroso-2-oxopropylcarbamate (NOPC) and ethyl N-nitroso-2-hydroxypropylcarbamate (NHPC), are useful models for predicting the DNA adducts observed in vivo following NDOPA treatment. Base-catalysed decomposition of NOPC in the presence of exogenous DNA yields five methylated purines (N3-, N7- and O6-methylguanines and N1- and N3-methyladenines). NHPC, a model for N-nitrosamines containing the 2-hydroxypropyl group, reacts with guanosine to yield N7- and O6-(2-hydroxypropyl)guanines.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
N-nitrosobis(2-oxopropyl)amine (NDOPA) induces pancreatic and liver tumors in hamsters. DNA analysis reveals methylation and 2-hydroxypropylation adducts, identifying key DNA damage mechanisms.
Area of Science:
- Carcinogenesis
- DNA adducts
- Chemical toxicology
Background:
- N-nitrosobis(2-oxopropyl)amine (NDOPA) is a known carcinogen that induces pancreatic duct adenocarcinomas in Syrian hamsters.
- Previous studies indicated NDOPA causes DNA methylation in hamster pancreas and liver.
Purpose of the Study:
- To elucidate the specific DNA adducts formed in vivo following NDOPA administration.
- To characterize the alkylation products in hamster liver and pancreatic DNA.
Main Methods:
- Administration of generally labeled tritiated NDOPA to Syrian hamsters.
- Isolation and identification of DNA adducts using chromatographic and spectroscopic techniques.
- In vitro studies using N-nitrosocarbamate models (NOPC and NHPC) with exogenous DNA and guanosine.
Main Results:
- Tritiated NDOPA studies revealed 2-hydroxypropylation as the primary three-carbon alkylation of hamster DNA.
- Identified N7-(2-hydroxypropyl)guanine and O6-(2-hydroxypropyl)guanine adducts in hamster liver DNA.
- Confirmed N7-methylguanine and O6-methylguanine in DNA from both liver and pancreas.
- In vitro models successfully predicted the formation of methylated and 2-hydroxypropylated purine adducts.
Conclusions:
- NDOPA induces DNA damage through both methylation and 2-hydroxypropylation in hamster organs.
- The identified adducts provide insights into the mechanism of NDOPA-induced carcinogenesis.
- N-nitrosocarbamate models are valuable for predicting in vivo DNA adduct formation.