Formation of strand breaks and interstrand cross‐links in DNA by methylglyoxal

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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.