title: Urinary analysis of 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine by isotope-dilution LC-MS/MS with automated solid-phase extraction: Study of 8-oxo-7,8-dihydroguanine stability.
abstract: A highly sensitive quantitative method based on LC-MS/MS was developed to simultaneously and directly measure 8-oxo-7,8-dihydroguanine (8-oxoGua) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in urine. It was found that 8-oxoGua could be artifactually generated from 8-oxodGuo during the ionization process by both in-source thermolysis and collisionally induced dissociation. Our method applied a two-stage wash procedure in the online solid-phase extraction system that not only eliminated ion suppression but also prevented artifactual interference with 8-oxoGua by 8-oxodGuo by eluting the analytes individually. With the use of isotope internal standards, the detection limits of 8-oxoGua and 8-oxodGuo were estimated to be 30 and 3.5 fmol, respectively. The 8-oxoGua stability under common storage conditions was first investigated. Dissolved 8-oxoGua in NaOH (pH 12) was quite fragile and stable for only <1 day at room temperature. When pH and temperature were reduced, the 8-oxoGua stability at -20 degrees C was significantly increased to approximately 87 days in water (pH approximately 7) and approximately 112 days when diluted in 5% methanol. This method was further applied to measure urinary samples of healthy subjects. A molar ratio of 8-oxoGua to 8-oxodGuo of approximately 4.6 was found, supporting the hypothesis that oxidatively damaged DNA is primarily repaired by the base excision repair pathway.
authors.affiliation: Department of Public Health, Chung Shan Medical University, Taichung 402, Taiwan. windyhu@csmu.edu.tw
authors.forename: Chiung-Wen
authors.initials: CW
authors.lastname: Hu
authors.forename: Mu-Rong
authors.initials: MR
authors.lastname: Chao
authors.forename: Ciao-Han
authors.initials: CH
authors.lastname: Sie
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000328:Adult; D002851:Chromatography, High Pressure Liquid; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000652:urine; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000652:urine; D006801:Humans; D008297:Male; D009587:Nitrogen Isotopes; D012016:Reference Values; D012680:Sensitivity and Specificity; D052616:Solid Phase Extraction; D053719:Tandem Mass Spectrometry; D013997:Time Factors
chemical_list: D009587:Nitrogen Isotopes; C024829:8-hydroxyguanine; D006147:Guanine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine