Abstract
We previously discovered that squalene monohydroperoxide (SQ-OOH) was produced on human forehead skin and suggested that skin squalene (SQ) may be the principal target lipid for oxidative stress (e.g., sunlight exposure). Because of 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 system. 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 LC-MS/MS with MRM, individual SQ-OOH isomers could be separated and detected with a sensitivity of 0.05 ng/injection. The total concentration of SQ-OOH isomers in forehead skin was approximately 956 microg/g skin lipids, but it increased up to 2,760 microg/g skin lipids after 3 h of sunlight exposure. The LC-MS/MS method was useful for investigating the peroxidation mechanisms of SQ as well as SQ-OOH-mediated skin disorders.
Highlights
We previously discovered that squalene monohydroperoxide (SQ-OOH) was produced on human forehead skin and suggested that skin squalene (SQ) may be the principal target lipid for oxidative stress
We and other researchers reported that using liquid chromatography-chemiluminescence detection (LC-CL), or the rather insensitive LC-UV detection method at 210 nm, SQ-OOH levels increased markedly in skin surface lipids from human forehead after exposure to sunlight [11] or UV A and B [12,13,14]
An alternative method for the complete structural characterization of SQ-OOH in vivo is required to understand the mechanisms of SQ peroxidation as well as SQ-OOH-mediated skin disorders
Summary
We previously discovered that squalene monohydroperoxide (SQ-OOH) was produced on human forehead skin and suggested that skin squalene (SQ) may be the principal target lipid for oxidative stress (e.g., sunlight exposure). We and other researchers reported that using LC-CL, or the rather insensitive LC-UV detection method at 210 nm, SQ-OOH levels increased markedly in skin surface lipids from human forehead after exposure to sunlight [11] or UV A and B [12,13,14]. These studies [7, 8, 10,11,12,13,14] suggested that SQ-OOH accumulation could be involved in inflammatory skin disorders such as skin cancer, cutaneous autoimmune disease, and skin aging.
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