Spectroscopic studies of the interaction of aspirin and its important metabolite, salicylate ion, with DNA, A·T and G·C rich sequences.

Among different biological effects of acetylsalicylic acid (ASA), its anticancer property is controversial. Since ASA hydrolyzes rapidly to salicylic acid (SA), especially in the blood, interaction of both ASA and SA (as the small molecules) with ctDNA, oligo(dA·dT)15 and oligo(dG·dC)15, as a possible mechanism of their action, is investigated here. The results show that the rate of ASA hydrolysis in the absence and presence of ctDNA is similar. The spectrophotometric results indicate that both ASA and SA cooperatively bind to ctDNA. The binding constants (K) are (1.7±0.7)×10(3) M(-1) and (6.7±0.2)×10(3) M(-1) for ASA and SA, respectively. Both ligands quench the fluorescence emission of ethidium bromide (Et)-ctDNA complex. The Scatchard plots indicate the non-displacement based quenching (non-intercalative binding). The circular dichroism (CD) spectra of ASA- or SA-ctDsNA complexes show the minor distortion of ctDNA structure, with no characteristic peaks for intercalation of ligands. Tm of ctDNA is decreased up to 3°C upon ASA binding. The CD results also indicate more distortions on oligo(dG·dC)15 structure due to the binding of both ASA and SA in comparison with oligo(dA·dT)15. All data indicate the more affinity for SA binding with DNA minor groove in comparison with ASA which has more hydrophobic character.

The value of DNA methylation analysis in basic, initial toxicity assessments.

DNA methylation is an epigenetic mechanism regulating patterns of gene expression. Our goal was to see if the assessment of DNA methylation might be a useful tool, when used in conjunction with initial, basic in vitro tests, to provide a more informative preliminary appraisal of the toxic potential of chemicals to prioritize them for further evaluation. We sought to give better indications of a compound's toxic potential and its possible mechanism of action at an earlier time and, thereby, contribute to a rational approach of an overall reduction in testing by making improved early decisions. Global and GC-rich patterns of DNA methylation were evaluated along with more traditional cytolethality measurements, e.g., cytolethality and genotoxicity assessments, on rat hepatoma (H4IIE) cells. The relative toxic potential of model compounds camptothecin, 5-fluorouracil, rotenone, and staurosporine was estimated by employing DNA methylation assessments combined with our cytolethality data plus genotoxicity information gleaned from the literature. The overall contribution of the methylation assessment was threefold; it (1) strengthened a ranking based on genotoxicity; (2) provided an indication that a compound might be more potentially problematic than what cytolethality and genotoxicity assessments alone would indicate; and (3) suggested that compounds, particularly nongenotoxins, that are more potent regarding their ability to alter methylation, especially at noncytolethal concentrations, may be more potentially toxic. Altered methylation per se is not proof of toxicity; this needs to be viewed as a component of an evaluation.