Mass Spectrometric Discrimination of Squalene Monohydroperoxide Isomers

et al. 2018

Sci Rep

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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.

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

Sci Rep

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“…Recently, we developed a method that enables the analysis of SQOOH isomers with high selectivity and sensitivity, and with the use of this method, the formation of SQOOH isomers by singlet oxygen oxidation and free radical oxidation was investigated. As a result, singlet oxygen oxidation of squalene was found to form six SQOOH isomers in nearly equal amounts, whereas free radical oxidation of squalene mainly formed SQOOH isomers bearing hydroperoxyl groups at terminal ends of the squalene chain (i.e., 2‐ and 3‐OOH‐SQ) .…”

Section: Resultsmentioning

confidence: 99%

“…Seven commercially available SLO supplements were obtained from local stores in Tokyo, Japan. SQOOH isomer standards were synthesized according to our previous study . Squalene was obtained from FUJIFILM Wako Pure Chemical (Osaka, Japan) and purified with semipreparative high‐performance liquid chromatography (HPLC) prior to use in oxidation experiments.…”

Section: Methodsmentioning

confidence: 99%

“…We previously reported the analysis of SQOOH isomers in human SSLs by using LC−MS/MS with atmospheric pressure chemical ionization (APCI), but due to the nature of APCI fragmentation, fragment ions with similar patterns were produced, making it difficult to selectively analyze SQOOH isomers . 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 .…”

Section: Introductionmentioning

confidence: 99%

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

Annals of the New York Academy of Sciences

et al. 2019

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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.

“…We were first able to achieve SQOOH isomer analysis by using LC-MS/MS with atmospheric pressure chemical ionization (APCI), but due to the nature of APCI fragmentation, fragment ions with similar patterns were produced, making it difficult to selectively analyze SQOOH isomers (35). Hence, we recently developed an improved method that enabled for the highly selective detection of six SQOOH isomers (39), based on evidence that the use of sodium ions during LC-MS/MS analysis enables the selective analysis of other lipid hydroperoxide isomers (40)(41)(42)(43). With the use of this method, it was identified that squalene oxidation by singlet oxygen oxidation and free radical oxidation yield different SQOOH isomers; singlet oxygen oxidation formed six SQOOH isomers in nearly equal amounts whereas free radical oxidation mainly formed 2-OOH-SQ and 3-OOH-SQ (44).…”

Section: Evaluation Of Squalene Oxidation Mechanisms: Lc-ms/ms Analysmentioning

confidence: 99%

Significance of Squalene in Rice Bran Oil and Perspectives on Squalene Oxidation

et al. 2019

J Nutr Sci Vitaminol

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As an intermediate metabolite during the biosynthesis of sterols, squalene is found ubiquitously in plants and animals. In rice, squalene is contained in rice bran, and consequently, squalene in rice bran oil has gained attention. Studies have shown that the intake of squalene from food sources demonstrate various physiological benefits such as the prevention of cancer and cardiovascular disease. Squalene is also known as an effective antioxidant in edible oils. However, due to its chemical structure, squalene is susceptible to oxidation, which may cause a decline in the nutraceutical and antioxidative effects of squalene in edible oils. Oxidative degradation of squalene also results in the formation of scission products (i.e., aldehydes and ketones) which may lead to off-flavor. Since the rate of squalene oxidation depends on the factors that induce its oxidation (i.e., light or heat), emphasis on oxidation mechanisms is necessary. It has been demonstrated in previous studies that the oxidation products formed by the singlet oxygen oxidation and free radical oxidation of squalene are different, and more recently, we demonstrated that different squalene monohydroperoxide isomers are formed by each oxidation mechanism. We herein discuss the significance of squalene in rice bran oil as well as the oxidative degradation of squalene in edible oils with focus on oxidation mechanisms.