Novel LC-ESI/MS/MS(n) method for the characterization and quantification of 2'-deoxyguanosine adducts of the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by 2-D linear quadrupole ion trap mass spectrometry

• Published in: Chemical research in toxicology Vol. 20; no. 2; p. 263
• Main Authors: Goodenough, Angela K, Schut, Herman A J, Turesky, Robert J
• Format: Journal Article
• Language: English
• Published: United States 01.02.2007
• Subjects: Animals; Carcinogens - administration & dosage; Carcinogens - chemistry; Carcinogens - metabolism; Chromatography, Liquid - methods; Colon - chemistry; Colon - drug effects; Colon - metabolism; Deoxyguanosine - analogs & derivatives; Deoxyguanosine - analysis; Deoxyguanosine - metabolism; Diet; DNA Adducts - analysis; DNA Adducts - metabolism; Female; Imidazoles - administration & dosage; Imidazoles - analysis; Imidazoles - toxicity; Kinetics; Liver - chemistry; Liver - drug effects; Liver - metabolism; Molecular Structure; Rats; Rats, Sprague-Dawley; Sensitivity and Specificity; Spectrometry, Mass, Electrospray Ionization - methods; Stereoisomerism; Tandem Mass Spectrometry - methods; Time Factors
• ISSN: 0893-228X
• DOI: 10.1021/tx0601713

An accurate and sensitive liquid chromatography-electrospray ionization/multi-stage mass spectrometry (LC-ESI/MS/MS(n)) technique has been developed for the characterization and quantification of 2'-deoxyguanosine (dG) adducts of the dietary mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). PhIP is an animal and potential human carcinogen that occurs in grilled meats. Following enzymatic digestion and adduct enrichment by solid-phase extraction (SPE), PhIP-DNA adducts were analyzed by MS/MS and MS(n) scan modes on a 2-D linear quadrupole ion trap mass spectrometer (QIT/MS). The major DNA adduct, N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (dG-C8-PhIP), was detected in calf thymus (CT) DNA modified in vitro with a bioactivated form of PhIP and in the colon and liver of rats given PhIP as part of the diet. The lower limit of detection (LOD) was 1 adduct per 10(8) DNA bases, and the limit of quantification (LOQ) was 3 adducts per 10(8) DNA bases in both MS/MS and MS(3) scan modes, using 27 microg of DNA for analysis. Measurements were based on isotope dilution with the internal standard, N-(deoxyguanosin-8-yl)-2-amino-1-(trideutero)methyl-6-phenylimidazo[4,5-b]pyridine (dG-C8-[2H3C]-PhIP). The selected reaction monitoring (SRM) scan mode in MS/MS was employed to monitor the loss of deoxyribose (dR) from the protonated molecules of the adducts ([M + H - 116]+). The consecutive reaction monitoring (CRM) scan modes in MS(3) and MS(4) were used to measure and further characterize product ions of the aglycone ion (BH2+) (Guanyl-PhIP). The MS(3) scan mode was effective in eliminating isobaric interferences observed in the MS/MS scan mode and resulted in an improved signal-to-noise (S/N) ratio. Moreover, the product ion spectra obtained by the MS(n) scan modes provided rich structural information about the adduct and were used to corroborate the identity of dG-C8-PhIP. In addition, an isomeric dG-PhIP adduct was detected in vivo. This LC-ESI/MS/MS(n) method is the first reported application on the use of the MS(3) scan mode for the analysis of DNA adducts in vivo.