Oxidation of squalene by singlet oxygen and free radicals results in different compositions of squalene monohydroperoxide isomers

Abstract

Oxidation of squalene (SQ) causes a decline in the nutritional value of SQ in foods, as well as an accumulation of SQ oxidation products in skin lipids which lead to adverse skin conditions. However, mechanistic insights as to how SQ is oxidized by different oxidation mechanisms have been limited, and thus effective measures towards the prevention of SQ oxidation have not been identified. In this study, we oxidized SQ by either singlet oxygen oxidation or free radical oxidation, and monitored the formation of the six SQ monohydroperoxide (SQOOH) isomers, the primary oxidation products of SQ, at the isomeric level. While singlet oxygen oxidation of SQ resulted in the formation of similar amounts of the six SQOOH isomers, free radical oxidation of SQ mainly formed two types of isomers, 2-OOH-SQ and 3-OOH-SQ. The addition of β-carotene during singlet oxygen oxidation, and the addition of α-tocopherol during free radical oxidation lead to a dose-dependent decrease in the formation of SQOOH isomers. Such results suggest that the analysis of SQOOH at the isomeric level allows for the determination of the cause of SQ oxidation in various samples, and provides a foothold for future studies concerning the prevention of SQ oxidation.

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

“…The following multiple reaction monitoring (MRM) pairs were utilized for the analysis of each SQOOH isomer: m/z 465.4 > 433.5, 2‐OOH‐SQ; m/z 465.4 > 395.3, 3‐OOH‐SQ; m/z 465.4 > 365.3, 6‐OOH‐SQ; m/z 465.4 > 297.2, 10‐OOH‐SQ; m/z 465.4 > 181.1, 7‐OOH‐SQ; m/z 465.4 > 229.2, 11‐OOH‐SQ. Other MS parameters, consistent with our previous study, were as follows: curtain gas, 30.0 psi; collision gas, 7.0 psi; ion spray voltage, 5500.0 V; temperature, 400.0 °C; ion source gas 1, 80.0 psi; and ion source gas 2, 60.0 psi. External calibration curves for quantitation were prepared with the use of synthetic SQOOH isomer standards.…”

“…Singlet oxygen and free radical oxidation of squalene were performed according to a previous report . For singlet oxygen oxidation, 100 µg of squalene was dissolved in 50 µL of ethanol/chloroform (1:1, v/v), to which 50 µL of a 20 mM EP solution in ethanol/chloroform (1:1, v/v) was added and incubated at 20 °C for 4 hours.…”

“…Analysis of SQOOH isomers was performed according to a previously described method with modifications to the HPLC part. A 4000 QTRAP ® mass spectrometer was equipped with an ExionLC TM HPLC/UHPLC system (SCIEX; Tokyo, Japan).…”

“…Thus, we recently developed an improved method that can selectively and sensitively analyze SQOOH isomers on the basis of evidence that the analysis of sodium adducts during LC−MS/MS analysis enables the selective analysis of other lipid hydroperoxide isomers . With the use of this method, we investigated the oxidation mechanisms of squalene and identified that singlet oxygen oxidation of squalene forms six SQOOH isomers in nearly equal amounts, whereas free radical oxidation mainly forms 2‐ and 3‐OOH‐SQ . In turn, such results suggested that the cause of squalene oxidation can be determined by examining the composition of SQOOH isomers in various samples.…”

The Effect of Temperature and Exposure Time on Stability of Cholesterol and Squalene in Latent Fingermarks Deposited on PVDF Membrane

“…In contrast, squalene has been shown to oxidize at lower temperatures than cholesterol. Specifically, Shimizu et al found that oxidation of squalene by heating is observed after incubation at 40, 50, and 60°C for 8 h. Frankel et al . also demonstrated the process of peroxide formation from squalene at 40 and 60 °C.…”