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Formation of strand breaks and interstrand cross-links in DNA by methylglyoxal
A Rahman1, Shahabuddin, S M Hadi
1Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, India.
Abstract:
Methylglyoxal (MG), a dietary mutagen, is present in various frequently consumed beverages and foods and in cigarette smoke. A combination of S1 nuclease hydrolysis and alkaline unwinding assay was used to demonstrate the formation of single-strand breaks and interstrand cross-links in DNA upon treatment with MG. Calf thymus DNA, when treated with increasing concentrations of MG, showed an increasing degree of S1 nuclease hydrolysis. It also showed the formation of an increasing number of strand breaks per molecule as determined by an alkaline unwinding assay. Incubation of DNA with relatively higher concentrations of methylglyoxal or prolonged treatment gave increased thermal melting temperatures and an enhanced rate of reannealing after thermal denaturation. These results indicated the formation of interstrand cross-links. Upon treatment with MG, A-T base pair depleted DNA showed a reduced number of single-strand break formation. It also showed a significantly lower decrease in Tm as compared with MG-treated normal DNA. These results showed that under the conditions used, MG primarily reacts with A-T base pairs in duplex DNA.
Insights
Methylglyoxal (MG), a dietary mutagen found in food and smoke, damages DNA by causing strand breaks and cross-links. Studies show MG primarily targets A-T base pairs in DNA.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Methylglyoxal (MG) is a reactive dicarbonyl compound found in various food items, beverages, and cigarette smoke.
- MG is recognized as a dietary mutagen with potential genotoxic effects on cellular DNA.
Purpose of the Study:
- To investigate the DNA damaging effects of methylglyoxal (MG).
- To elucidate the specific types of DNA lesions induced by MG, including strand breaks and cross-links.
- To determine the preferential binding sites of MG within the DNA duplex.
Main Methods:
- Treatment of calf thymus DNA with varying concentrations of methylglyoxal (MG).
- Assessment of DNA damage using S1 nuclease hydrolysis to detect single-strand breaks.
- Quantification of DNA strand breaks and interstrand cross-links via alkaline unwinding assays.
- Analysis of DNA structural changes using thermal melting (Tm) and reannealing kinetics.
Main Results:
- Increasing MG concentrations led to a higher degree of S1 nuclease hydrolysis, indicating increased single-strand breaks.
- Alkaline unwinding assays confirmed a dose-dependent increase in strand breaks per DNA molecule.
- Elevated MG concentrations or prolonged incubation resulted in increased Tm and enhanced reannealing rates, signifying interstrand cross-link formation.
- DNA depleted of A-T base pairs exhibited reduced single-strand break formation and a smaller decrease in Tm compared to normal DNA treated with MG.
Conclusions:
- Methylglyoxal (MG) induces both single-strand breaks and interstrand cross-links in DNA.
- The formation of DNA lesions by MG is concentration-dependent.
- MG preferentially reacts with adenine-thymine (A-T) base pairs in duplex DNA under the experimental conditions.