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DNA adducts, mutant frequencies and mutation spectra in lambda lacZ transgenic mice treated with
V L Souliotis1, J H van Delft, M J Steenwinkel
1Laboratory of Chemical Carcinogenesis, Institute of Biological Research and Biotechnology, National Hellenic Research Foundation, Athens, Greece.
Abstract:
Groups of lambda lacZ transgenic mice were treated i.p. with N-nitrosodimethylamine (NDMA) as single doses of 5 mg/kg or 10 mg/kg or as 10 daily doses of 1 mg/kg and changes in DNA N7- or O6-methylguanine or the repair enzyme O6-alkylguanine-DNA alkyltransferase (AGT) were followed for up to 14 days in various tissues. Adduct induction in the liver exceeded by at least one order of magnitude than observed in the next nearest target tissue (lung), and was approximately linearly related to dose, except for O6-methylguanine after the first dose of 1 mg/kg which was lower than expected. Substantial induction of lambda lacZ mutagenesis was observed only in the liver, where the mutant frequency was already maximal within 7 days after 5 mg/kg NDMA and remained unchanged thereafter up to 49 days. Small but marginally significant increases in mutant frequency were consistently observed in the spleen after all three modes of treatment. A lack of proportionality between mutation induction and the administered dose or the corresponding adduct levels was observed, probably reflecting the importance of toxicity-related cell proliferation caused by NDMA at higher doses. Twenty eight days after a dose of 10 mg/kg (causing a 3.6-fold increase in mutant frequency), NDMA was found to increase the frequency of GC-->AT mutations (with a concomitant shift of their preferential location from CpG sites to GpG sites), which made up approximately 60% of the induced mutations. Surprisingly, NDMA also caused a significant increase in deletions of a few (up to 11) base-pairs (22%).
Insights
N-nitrosodimethylamine (NDMA) induces liver mutations in mice, with adducts and mutations showing a dose-response relationship. NDMA causes GC to AT mutations and DNA deletions, highlighting its genotoxic effects.
Area of Science:
- Toxicology
- Genetics
- Molecular Biology
Background:
- N-nitrosodimethylamine (NDMA) is a known carcinogen.
- Understanding the genotoxic mechanisms of NDMA is crucial for risk assessment.
Purpose of the Study:
- To investigate the induction of DNA adducts, mutations, and the repair enzyme O6-alkylguanine-DNA alkyltransferase (AGT) in mice treated with NDMA.
- To determine the dose-response relationship and tissue specificity of NDMA-induced genotoxicity.
Main Methods:
- Lambda lacZ transgenic mice were administered single or multiple doses of NDMA.
- DNA adducts (N7- and O6-methylguanine) and AGT levels were measured in various tissues.
- Mutant frequency in the liver and spleen was assessed using the lambda lacZ assay.
Main Results:
- Liver showed significantly higher adduct induction compared to other tissues.
- NDMA induced lambda lacZ mutagenesis primarily in the liver, with a dose-dependent increase in mutant frequency.
- A lack of proportionality between adduct levels and mutation induction suggested the role of toxicity and cell proliferation.
- NDMA treatment resulted in GC to AT mutations and increased DNA deletions.
Conclusions:
- NDMA is a potent genotoxic agent, primarily targeting the liver.
- The study elucidates the specific types of mutations induced by NDMA, including base substitutions and deletions.
- Findings underscore the importance of considering cell proliferation in assessing chemical genotoxicity.