Detection of 7-(2′-Carboxyethyl)guanine but not 7- carboxymethylguanine in human liver DNA

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7-Carboxymethylguanine (7-CMGua) and 7-(2′-carboxyethyl)guanine (7-CEGua) are DNA adducts that potentially could be formed upon the metabolism of the carcinogenic nitrosamines N-nitrososarcosine (NSAR) and 3-(methylnitrosamino)propionic acid (MNPA), respectively, or from other sources such as nitrosation of glycine (7-CMGua) or reaction of DNA with acrylic acid (7-CEGua). Since both NSAR and MNPA have been detected in human urine and there are plausible sources of exposure to other precursors to these adducts, we analyzed human liver DNA for 7-CMGua and 7-CEGua, using liquid chromatography-electrospray ionization-tandem mass spectrometry-selected reaction monitoring (LC-ESI-MS/MS-SRM). Human hepatic DNA was mixed with [ 15N5]7-CMGua and [15N5]7-CEGua as internal standards and enzymatically hydrolyzed. The hydrolysate was partially purified by solid-phase extraction, and the resulting fraction was treated with acetyl chloride in methanol to convert 7-CMGua and 7-CEGua to their methyl esters. After a second solid-phase extraction, LC-ESI-MS/MS-SRM analysis was carried out using the transitions m/z 224 [M + H]+ → m/z 164 [(M + H) - HCOOCH3]+ and m/z 238 [M + H]+ → m/z 152 [BH]+ for the methyl esters of 7-CMGua and 7-CEGua, respectively. The method was sensitive, accurate, precise, and apparently free from artifact formation. 7-CEGua, as its methyl ester, was detected in all 24 human liver samples analyzed, mean ± SD, 373 ± 320 fmol/μmol Gua (74.6 adducts per 109 nucleotides), range 17-1189 fmol/μmol Gua, but the methyl ester of 7-CMGua was not detected in any sample. These results demonstrate the ubiquitous presence of 7-CEGua in human liver DNA. Acrylic acid may be a likely endogenous precursor to 7-CEGua.

Original languageEnglish (US)
Pages (from-to)1089-1096
Number of pages8
JournalChemical research in toxicology
Issue number6
StatePublished - Jun 21 2010


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