Low sensitivity of the comet assay to detect acetaldehyde-induced genotoxicity

Acetaldehyde (AA) is known to induce DNA-protein cross-links (DPX) and other genotoxic and mutagenic effects in cultured mammalian cells. Compared to formaldehyde (FA), AA is a very weak inducer of DPX and increased DPX levels are only measured at high, cytotoxic concentrations by different methods. Besides DPX, AA also induces DNA-DNA cross-links. Because the comet assay is increasingly used for the detection of cross-linking agents, we characterized the effects of AA in the comet assay in relation to cytotoxicity and other genetic endpoints such as the induction of sister chromatid exchange (SCE) and micronuclei (MN). The standard alkaline comet assay did not indicate induction of DNA strand-breaks by AA in a range of concentrations from 0.2 to 20 mM. AA at a concentration of 20 mM was clearly cytotoxic and reduced cell growth and population doubling to less than 50% of the control. Using the comet assay modification with proteinase K, slightly enhanced DNA migration was measured in comparison to treatment with AA only. No significant induction of cross-links by AA (measured as reduction of gamma ray-induced DNA migration) was determined by the comet assay. A small and reproducible but statistically not significant effect was measured for the AA concentration 20 mM. A clear and concentration-related increase in the frequency of sister chromatid exchange (SCE) and micronuclei (MN) was already measured at lower concentrations (0.2 and 0.5 mM, respectively). These results suggest that the comet assay has a low sensitivity for the detection of AA-induced DNA lesions leading to the induction of SCE and MN.