Submitted on June 18, 2007
Revised on September 7, 2007
Accepted on September 10, 2007
Ion-trap tandem mass spectrometric analysis of squalene monohydroperoxide isomers in sunlight-exposed human skin
Kiyotaka Nakagawa, Daigo Ibusuki, Yoshihiro Suzuki, Shinji Yamashita, Ohki Higuchi, Shinichi Oikawa, and Teruo Miyazawa
Graduate School of Agricultural Science, Tohoku University, Sendai, Miyagi 981-8555
Corresponding Author: miyazawa{at}biochem.tohoku.ac.jp
We previously discovered that squalene-monohydroperoxide (SQ-OOH) was produced on the human forehead skin, and suggested that skin squalene (SQ) may be the principal target lipid for oxidative stress (e.g., sunlight exposure). Due to its six double bonds, SQ peroxidation can yield various positional hydroperoxide isomers. However, the structural characterization of skin SQ-OOH isomers has never been reported. Here, we prepared pure SQ-OOH isomers, and developed an analytical method for SQ-OOH isomers using a quadrupole/linear ion-trap mass spectrometer, QTRAP MS/MS. Collision-induced dissociation produced specific fragment ions for each SQ-OOH isomer, which permitted discrimination between SQ-OOH isomers by multiple reaction monitoring (MRM). When lipid extract from human forehead skin was subjected to liquid chromatography (LC)-MS/MS with MRM, individual SQ-OOH isomers could be separated and detected with sensitivity of 0.05 ng/injection. The total concentration of SQ-OOH isomers in forehead skin was around 956 microgram/g skin lipids, but increased up to 2760 microgram/g skin lipids after 3 h sunlight exposure. The LC-MS/MS method was useful for investigating the peroxidation mechanisms of SQ, as well as SQ-OOH-mediated skin disorders.
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