DNA DAMAGE INDUCED BY PHOTOSENSITIZERS IN CELLULAR AND CELL-FREE SYSTEMS

Citation
B. Epe et al., DNA DAMAGE INDUCED BY PHOTOSENSITIZERS IN CELLULAR AND CELL-FREE SYSTEMS, MUTATION RESEARCH, 299(3-4), 1993, pp. 135-145
Citations number
61
Categorie Soggetti
Genetics & Heredity",Toxicology
Journal title
ISSN journal
00275107
Volume
299
Issue
3-4
Year of publication
1993
Pages
135 - 145
Database
ISI
SICI code
0027-5107(1993)299:3-4<135:DDIBPI>2.0.ZU;2-3
Abstract
The specific recognition of DNA modifications by repair endonucleases was used to characterize the DNA damage induced by photosensitizers in the presence of visible light. Under cell-free conditions, chemically unrelated photosensitizers (methylene blue, acridine orange, proflavi n, riboflavin, hematoporphyrin) induce the same type of DNA damage. It is characterized by a high number of base modifications sensitive to the repair endonuclease FPG protein (formamidopyrimidine-DNA glycosyla se), while both the number of DNA strand breaks and the number of site s of base loss (sensitive to exonuclease III or endonuclease IV) is lo w. Therefore the damage is markedly different from that induced by hyd roxyl radicals. Mechanistically, the generation of the base modificati ons sensitive to FPG protein involves singlet oxygen in some, but poss ibly not all cases, as substituting D2O for H2O increases the reaction yield six-fold in the case of methylene blue, but only 1.4-fold in th e case of acridine orange. In plasmids from Salmonella typhimurium str ains treated with methylene blue or acridine orange plus light and fro m Escherichia coli strains treated with acridine orange or proflavin p lus light, the same type of damage was observed as under cell-free con ditions. In L1210 mouse leukemia cells exposed to acridine orange plus light, the numbers of modifications sensitive to FPG protein and exon uclease Ill were quantified, in addition to strand breaks, by a modifi ed alkaline elution assay. Again, the number of base modifications sen sitive to FPG protein was found to be several-fold higher than the num ber of strand breaks and sites of base loss. It has to be concluded th at the DNA damage in the intact cells is not mediated by hydroxyl radi cals or cellular nucleases, but by the same mechanism as operates unde r cell-free conditions with these agents.