DNA damage and cell lethality by photodynamically-produced oxygen radicals

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dc.contributor.advisorSass, Ronald L.en_US
dc.creatorBurch, Paula Ellenen_US
dc.date.accessioned2009-06-04T00:29:54Zen_US
dc.date.available2009-06-04T00:29:54Zen_US
dc.date.issued1989en_US
dc.description.abstractSynthetic dyes, including thiazines, acridines, xanthenes, and a phenazine, were used as models for studying the photodynamic effect. In the presence of physiological reductants, the illuminated dyes produced superoxide (O$\sb2\sp-$), hydrogen peroxide (H$\sb2$O$\sb2$), and hydroxyl free radical (OH). Suitable reductants included NADH, glutathione, GMP, cysteine, tryptophan, and tyrosine. The production of OH$\cdot$ was dependent on chelated iron or on copper. Effective iron chelators included EDTA, DTPA, dipyridyl, and phenanthroline, and biologically significant compounds such as ATP, ADP, succinate, citrate, and DNA. DNA intercalation of the dyes did not prevent oxidization of NADH or the production of O$\sb2\sp-$ or OH$\cdot$. Hydroxyl radical scavengers competed effectively in the assays for the OH$\cdot$. While in the Haber-Weiss reaction superoxide reduces iron, which is oxidized by H$\sb2$O$\sb2$ to produce OH$\cdot$, excited state reduced dyes appeared capable of reducing the iron, so that SOD was only partially inhibitory of OH$\cdot$ production. Catalase prevented production of OH$\cdot$. Similar results were found for substrates and metals in an assay of single strand scission of DNA mediated by the dyes. Amounts of strand scission seen were dependent on concentrations of iron or dye. Cysteine, NADH, GTP, dGMP, tryptophan, and tyrosine were all able to provide electrons for the strand scission reaction. Furthermore, the single strand scission of DNA by the dyes was prevented by scavengers of O$\sb2\sp-$, H$\sb2$O$\sb2$ or OH$\cdot$ which are poor scavengers for singlet oxygen ($\sp1$O$\sb2$), and substitution of deuterium oxide for water, which exacerbates any damage produced by $\sp1$O$\sb2$, did not increase damage. The physiological reductant glutathione in E. coli was depleted by exposure to illuminated dye. Lethality of the dyes was reduced by enhanced levels of catalase or endonulcease IV provided by plasmid-coded genes, indicating that H$\sb2$O$\sb2$ is an important mediator of toxicity and that DNA is an important target, while OH$\cdot$ scavengers prevented kill, indicating that the OH$\cdot$ is also an important mediator of phototoxicity. Finally, DNA damage in vivo was reduced by an OH$\cdot$ scavenger. In conclusion, toxicity in the photodynamic effect is mediated by reduced oxygen species, particularly OH$\cdot$, and DNA damage probably underlies this toxicity.en_US
dc.format.extent224 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoThesis Biol. 1989 Burchen_US
dc.identifier.citationBurch, Paula Ellen. "DNA damage and cell lethality by photodynamically-produced oxygen radicals." (1989) Diss., Rice University. <a href="https://hdl.handle.net/1911/16213">https://hdl.handle.net/1911/16213</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16213en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectBiologyen_US
dc.subjectRadiologyen_US
dc.subjectMolecular biologyen_US
dc.subjectHealth sciencesen_US
dc.titleDNA damage and cell lethality by photodynamically-produced oxygen radicalsen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentBiologyen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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