Evaluation of squalene oxidation mechanisms in human skin surface lipids and shark liver oil supplements

Abstract

Squalene is a terpenoid found in human skin surface lipids (SSLs) and foods that possesses beneficial properties. However, since oxidation of squalene causes various complications, it is necessary to identify the mechanisms by which squalene is oxidized. In this study, we aimed to determine the oxidation mechanisms of squalene in SSLs and shark liver oil (SLO) supplements by the analysis of squalene monohydroperoxide (SQOOH) isomers, on the basis of our previous finding that different oxidation mechanisms yield different SQOOH isomers. Liquid chromatography–tandem mass spectrometry analysis of SQOOH isomers revealed that squalene in human SSLs was oxidized by singlet oxygen oxidation, whereas squalene in SLO was oxidized mainly by free radicals. As a result, we have presented the first evidence suggesting that the analysis of SQOOH isomers enables estimation of oxidation mechanisms. Estimating oxidation mechanisms by analyzing SQOOH isomers may provide a foundation for the prevention of skin diseases and food deterioration via regulation of squalene oxidation.

Novel Photoinduced Squalene Cyclic Peroxide Identified, Detected, and Quantified in Human Skin Surface Lipids

“…The rest of the fraction was evaporated and dissolved in 70% methanol and purified using an equilibrated C18 cartridge (Strata C18-E, 55 µm, 70 A, 100 mg, 1 mL. Phenomenex, Torrance, CA, USA) [ 26 ]. The obtained eluate was evaporated then dissolved in 950 µL hexane.…”

“…Over the years, lipid hydroperoxides and their mechanism of formation have been extensively studied as primary products of lipid oxidation, and they have long been linked to different pathogenesis such as accelerated aging, and inflammatory diseases [ 23 , 24 , 25 ]. Similarly, due to the terpenic nature of SQ, it has been reported to undergo singlet oxygen ( 1 O 2 ) oxidation on the skin to yield six SQ-monohydroperoxides (SQ-OOH) isomers as its primary oxidation products ( Figure 1 ) [ 26 ]. Previously, we demonstrated that the six SQ-OOH isomers increased following the exposure of the skin to sunlight, further confirming the photosensitized 1 O 2 oxidation of SQ [ 27 ].…”

Linoleic acid and squalene are oxidized by discrete oxidation mechanisms in human sebum

“…The analysis of the structural isomers of SQOOH supported previous reports suggesting that SQ is oxidized by singlet oxygen oxidation in human sebum. [9][10][11][12]26,27 Considering these results, it was interesting to note that LA and SQ are oxidized by discrete oxidation mechanisms in human sebum.…”

“…Sebum was collected from the forehead of healthy individuals with no evidence of skin abnormalities using acetone-soaked cotton swabs, as previously described. 9 After the collection of sebum with cotton swabs, the cotton tip of the swab was cut off, and sebum was extracted with 20 mL of chloroform. Experiments were conducted in accordance with the Declaration of Helsinki, and the protocols were approved by the ethics committee of Tohoku University Graduate School of Agricultural Science (registration numbers: 19-A-08 and 20-A-05) and the Shiba Palace Clinic Ethics Review Committee (registration number: 144023_rn-27497).…”

“…Sebum is composed of several lipid classes, such as triacylglycerols (TG), fatty acids (FA), wax esters (WE), squalene (SQ), and cholesterol esters (CE) 1,2 . It is established that these lipids are oxidized in response to external oxidative stimuli; for example, sunlight can cause photooxidation (singlet oxygen oxidation), and atmospheric oxygen can induce autoxidation (free radical oxidation) 3–9 . Among the lipids that constitute sebum, SQ has been extensively studied for its oxidation.…”