— The ability of the antibacterial agent dioxidine to generate the superoxide anion radical in E. coli cells, induce an SOS response, or cause DNA fragmentation or death of bacteria, as well as the effect of antioxidants on the processes listed, were studied using E. coli luminescent biosensors. Dioxidine induced the SOS response in the pColD-lux biosensor in concentrations typical for the most efficient induction of luminescence in a pSoxS-lux biosensor, the intensity of which depends on the amount of superoxide in the cell. Dioxidine in concentrations of more than 0.001 mol/L caused a decrease in the survival of bacterial cells, which is accompanied by the degradation of their DNA (as demonstrated by electrophoretic analysis). DNA degradation increased with an increase in the dioxidine concentration and decreased in the presence of the antioxidants glutathione and acetylcysteine. Antioxidants weakened the induction of the SOS response by dioxidine, as well as generation of superoxide radicals. Likely mechanisms of the formation of the hydroxyl radical during the reduction of the dioxidine NO group by bacterial reductases are discussed.

A comparative study of the genotoxic effects of methylmethanesulfonate (MMS) and epichlorohydrin (ECH) was performed using bacterial E. coli biosensors and the comet assay method in mice. ECH was shown to induce weaker SOS response and expression of the alk A gene in bacterial cells compared to MMS. In vivo experiments on mice using the comet assay method showed DNA-damaging activity of ECH in cells of the liver, kidneys, and lungs after 3 h of exposure, same as of MMS. The levels of DNA damage caused by ECH in these organs after exposure for 3 h were lower than for MMS. The genotoxic effect of ECH after 18 h of exposure was statistically significant only in a dose of 20 mg/kg in kidney cells.

8-Methoxypsoralen (8-MOP) is used for photochemotherapy of psoriasis and vitiligo. In therapy, called PUVA therapy, the affected skin of a patient who has previously been prescribed 8-MOP is irradiated with UV-A (> 320 nm). As a result of the photochemical reaction, 8-MOP forms a covalent bond with the pyrimidine bases of DNA and forms both monofunctional and bifunctional adducts. The latter cause 8-MOP-mediated cytotoxicity, leading to the death of psoriatic cells. However, in surviving cells, these same adducts can cause 8-MOP genotoxicity. For a comparative study of the cytotoxicity and genotoxicity of 8-MOP, the E. coli MG1655 lux biosensor (pColD-lux), carrying a recombinant plasmid with a lux operon controlled by the colD gene promoter, was first used. The colD gene (cda) is part of the E. coli SOS-regulon, which provides DNA repair and cell resistance to DNA damage. The death of bacteria was taken into account as an indicator of the cytotoxicity of 8-MOP+UV-A, and the death of bacteria was taken into account by the change in the luminescence intensity of the biosensor. Induction of 8-MOP-mediated SOS-response in bacteria depends on the dose of UV-A, and on the concentration of 8-MOP. At high UV-A doses, a 25-fold decrease in the survival of bacterial cells was detected (from 2 × 108 to 8 × 106 CFU), and in viable cells, an increase in the intensity of the SOS response by 675 times in terms of 106 cells. Thus, it was shown that in the bacterial test system, the genotoxic effect of 8-MOP is several times higher than its cytotoxicity. Key words: 8-methoxypsoralen, lux biosensor, E. coli, colD gene promoter, SOS response, UV radiation, adducts.