Singlet oxygen as an ultimately reactive species in Salmonella typhimurium DNA damage induced by methylene blue/visible light

Abstract

The specific recognition of various DNA modifications by repair enzymes is exploited for the analysis of DNA damage induced by visible light in the presence of methylene blue in Salmonella typhimurium. The relative frequencies of various endonuclease-sensitive sites and strand breaks are determined in the plasmid pAQ1 of the treated bacteria and are compared with those observed after exposure of isolated DNA to various conditions. This comparison of damage profiles indicates that the cellular DNA damage by illumination in the presence of methylene blue is caused predominantly by the direct action of singlet oxygen. Indirect mechanisms, e.g. involving a generation of superoxide and hydroxyl radicals or the activation of cellular nucleases, do not contribute very much. The damage is dominated by base modifications. These are subject to an efficient repair that is not mediated by uvrABC proteins and therefore most probably involves recognition by specific glycosylases. Revertant frequencies observed under these conditions in the strains TA1535, TA100, TA2638 and TA104 indicate a pronounced mutagenicity of the lesions induced. On the other hand, the DNA damage does not contribute significantly to the cytotoxicity caused by the treatment as an excision repair deficiency (uvrB) has no influence on cell killing.

DNA damage by singlet oxygen and cellular protective mechanisms

“…Direct cell treatment with agents that generate 1 O 2 is biased, as most of the damage may result from 1 O 2 reactivity to cell components other than genetic material, such as cell membranes. Nevertheless, cell death and mutagenesis were reported in Salmonella typhimurium bacterial strains (including wild type and uvrB mutants) treated with the photosensitizer methylene blue and light [86]. Additionally, the treatment of Escherichia coli strains with NDPO 2 also induced cell death and mutagenesis, detected with the induction of rifampicin resistant colonies.…”

White Light-mediated DNA Strand Breaks in Lens Epithelial Cells

“…Exposure to light in mammalian cells can lead to DNA damage, the severity of which is dependent on the wavelength and the internal and external cellular environment (Epe et al, 1989;Balasubramanian, 2000;Yusifov et al, 2000;Pavilack and Brod, 2001). Lens epithelial cells provide a good model for relatively early age-related increase in oxidative stress (Wolf and Penn, 2001).…”

Mutations induced by methylene blue plus light in single-stranded M13mp2.

“…Further studies indicated that the alterations in MB-treated DNA occur almost exclusively at deoxyguanosine (dGuo) residues (13,16) and proceeds through a singlet oxygen intermediate to yield primarily 8-hydroxydeoxyguanosine (8-oxodGuo) as one product of at least four products (17)(18)(19). There is also the possibility that other modified dGuo moieties are produced (20), as evidenced by the ability of Escherichia coli Fpg protein (21,22) to excise various dGuo adducts from DNA and the presence of an analogous enzyme in mammalian cells (ref. 23; J. Laval, personal communication).…”