Preparation of saturated fatty acid hydroperoxide isomers and determination of their thermal decomposition products - 2-alkanones and lactones

As known for quite a long time now, even saturated fatty acids can be oxidized at high temperatures to produce unique aroma compounds, such as 2-alkanones and lactones. Hydroperoxide positional isomers with a hydroperoxy group at the 2-, 3-, 4-, or 5-position are hypothesized to be responsible for the formation of these aroma components, but this hypothesis has not been verified. For the first time, this study successfully prepared a series of glyceryl trioctanoate hydroperoxide (C8TG;OOH) isomers. The isomers were thermally decomposed, proving that 2-heptanone was selectively formed from C8TG;3-OOH, and γ- and δ-octalactones were mainly formed from C8TG;4- and 5-OOH, respectively. C8TG;2-OOH was also involved in lactone formation, whereas C8TG;6- and 7-OOH were not. This proves the long-standing hypothesis. The mechanism revealed in this work is expected to be useful to create favorable aromas (i.e., 2-alkanones and lactones) from saturated fatty acids.

Induction of ferroptosis in human keratinocyte HaCaT cells by squalene hydroperoxide: Possible prevention of skin ferroptosis by botanical extracts

Ever since the proposal of ferroptosis, it has been studied as a nonapoptotic cell death caused by iron ion-dependent phospholipid (PL) peroxidation. We previously showed that treatment of human hepatoma cell line HepG2 with prepared PL hydroperoxide (PLOOH) resulted in ferroptosis. However, in human sebum, the major hydroperoxide is not PLOOH but squalene hydroperoxide (SQOOH), and to our knowledge, it is not established yet whether SQOOH induces ferroptosis in the skin. In this study, we synthesized SQOOH and treated human keratinocyte HaCaT cells with SQOOH. The results showed that SQOOH induces ferroptosis in HaCaT cells in the same way that PLOOH causes ferroptosis in HepG2 cells. Some natural antioxidants (botanical extracts) could inhibit the ferroptosis in both the cell types. Consequently, future research focus would revolve around the involvement of SQOOH-induced ferroptosis in skin pathologies as well as the prevention and treatment of skin diseases through inhibition of ferroptosis by botanical extracts.

Higher Cholesterol Absorption Marker at Baseline Predicts Fewer Cardiovascular Events in Elderly Patients Receiving Hypercholesterolemia Treatment: The KEEP Study

BACKGROUND

Higher cholesterol absorption has been reported to be related to a higher incidence of cardiovascular events (CVEs). The KEEP (Kyushu Elderly Ezetimibe Phytosterol) study, a substudy of the EWTOPIA 75 (Ezetimibe Lipid-Lowering Trial on Prevention of Atherosclerotic Cardiovascular Disease in 75 or Older) study, investigated the relationships of cholesterol absorption and synthesis markers with CVEs in older old individuals with hypercholesterolemia, particularly in relation to ezetimibe treatment.

METHODS AND RESULTS

Eligible patients were those aged ≥75 years who had low-density lipoprotein cholesterol ≥140 mg/dL, no history of coronary artery disease, and no recent use of lipid-lowering drugs. Participants were randomly assigned into a diet-only or diet-plus-ezetimibe group. Baseline and 24-week follow-up blood samples were analyzed for cholesterol absorption (eg, campesterol) and synthesis markers (eg, lathosterol). Of 1287 patients, 1061 patients with baseline measurement were analyzed. Over a median follow-up of 4.0 years, 64 CVEs occurred. Higher campesterol levels at baseline were significantly associated with a lower risk of CVEs. After adjustment for sex, age, and treatment, the hazard ratios for the lowest to highest quartile categories of baseline campesterol were 1.00 (reference), 0.59 (95% CI, 0.30-1.17), 0.44 (95% CI, 0.21-0.94), and 0.44 (95% CI, 0.21-0.93), respectively (trend P=0.01). This association persisted after further adjustment for hypertension, diabetes, and other cardiovascular risk factors. Neither interactions with ezetimibe treatment nor mediating effects of the changes in cholesterol absorption markers were observed.

CONCLUSIONS

The KEEP study indicated that higher campesterol levels without lipid-lowering drugs were associated with a lower incidence of CVEs in older old individuals with hypercholesterolemia who were subsequently treated with diet or ezetimibe.

REGISTRATION

URL: https://www.umin.ac.jp; unique identifier: UMIN000017769.

LC-MS/MS analysis of milk triacylglycerol hydroperoxide isomers which are generated corresponding to the photo- and thermal-oxidation

Milk is a rich source of essential nutrients such as lipids. However, lipid oxidation can be considered a crucial factor in determining the initial stage of milk deterioration. Therefore, it is essential to identify the mechanisms of lipid oxidation, such as photo-oxidation or thermal oxidation, to efficiently prevent it by selecting proper antioxidants. In this study, the oxidation mechanisms of long-life (LL) milk were investigated, and triacylglycerol hydroperoxide isomers generated corresponding to the oxidation mechanisms were analyzed by LC-MS/MS. This study first prepared the standard of TG 4:0_16:0_18:1;OOH isomers, which are the appropriate target for evaluating LL milk's oxidation mechanism. The authentic standards provided the robust analysis of TG 4:0_16:0_18:1;OOH isomers and suggested that LL milk was susceptible to photo-oxidation rather than thermal-oxidation. Furthermore, it was discovered that radicals play a role in the oxidation of LL milk during photo-oxidation. This information could be valuable in effectively preventing photo-oxidation in LL milk. It is important to note that milk is contained in a variety of food products. Hence, these findings would be applicable not only to milk but also to various milk-containing food products.

Analysis of docosahexaenoic acid hydroperoxide isomers in mackerel using liquid chromatography-mass spectrometry

Docosahexaenoic acid (DHA) is mostly esterified in food and is easily oxidized by exposure to heat or light. Hydroperoxide positions of DHA mono-hydroperoxide (DHA;OOH) provide information on oxidation mechanisms (e.g., radical- or singlet oxygen oxidation), yet direct identification of esterified DHA;OOH isomers has not been achieved. We previously accomplished the direct analysis of free DHA;OOH isomers with liquid chromatography-mass spectrometry (LC-MS/MS). In this study, we developed an LC-MS/MS method for direct analysis of esterified DHA;OOH based on our previous study. The developed method was capable of distinguishing esterified DHA;OOH isomers in raw- and oxidized mackerel. The result suggested that radical oxidation of esterified DHA can progress even in refrigeration. Different transitions were observed depending on the oxidation mechanism and lipid class. The analytical method and insights obtained in this study would be valuable to further understand and effectively prevent DHA oxidation in food products.

Dietary triacylglycerol hydroperoxide is not absorbed, yet it induces the formation of other triacylglycerol hydroperoxides in the gastrointestinal tract

The in vivo presence of triacylglycerol hydroperoxide (TGOOH), a primary oxidation product of triacylglycerol (TG), has been speculated to be involved in various diseases. Thus, considerable attention has been paid to whether dietary TGOOH is absorbed from the intestine. In this study, we performed the lymph duct-cannulation study in rats and analyzed the level of TGOOH in lymph following administration of a TG emulsion containing TGOOH. As we successfully detected TGOOH from the lymph, we hypothesized that this might be originated from the intestinal absorption of dietary TGOOH [hypothesis I] and/or the in situ formation of TGOOH [hypothesis II]. To determine the validity of these hypotheses, we then performed another cannulation study using a TG emulsion containing a deuterium-labeled TGOOH (D2-TGOOH) that is traceable in vivo. After administration of this emulsion to rats, we clearly detected unlabeled TGOOH instead of D2-TGOOH from the lymph, indicating that TGOOH is not absorbed from the intestine but is more likely to be produced in situ. By discriminating the isomeric structures of TGOOH present in lymph, we predicted the mechanism by which the intake of dietary TGOOH triggers oxidative stress (e.g., via generation of singlet oxygen) and induces in situ formation of TGOOH. The results of this study hereby provide a foothold to better understand the physiological significance of TGOOH on human health.

Elucidation of Olive Oil Oxidation Mechanisms by Analysis of Triacylglycerol Hydroperoxide Isomers Using LC-MS/MS

Despite the importance of the insight about the oxidation mechanisms (i.e., radical and singlet oxygen (¹O₂) oxidation) in extra virgin olive oil (EVOO), the elucidation has been difficult due to its various triacylglycerol molecular species and complex matrix. This study tried to evaluate the mechanisms responsible for EVOO oxidation in our daily use by quantitative determination of triacylglycerol hydroperoxide (TGOOH) isomers using LC-MS/MS. The standards of dioleoyl-(hydroperoxy octadecadienoyl)-triacylglycerol and dioleoyl-(hydroperoxy octadecamonoenoyl)-triacylglycerol, which are the predominant TGOOHs contained in EVOO, were prepared. Subsequently, fresh, thermal-, and photo-oxidized EVOO were analyzed. The obtained results mostly agreed with the previously reported characteristics of the radical and ¹O₂ oxidation of linoleic acid and oleic acid. This suggests that the methods described in this paper should be valuable in understanding how different factors that determine the quality of EVOO (e.g., olive species, cultivation area, cultivation timing, and extraction methods) contribute to its oxidative stability.

Investigation of Lipoproteins Oxidation Mechanisms by the Analysis of Lipid Hydroperoxide Isomers

The continuous formation and accumulation of oxidized lipids (e.g., lipid hydroperoxides (LOOH)) which are present even in plasma lipoproteins of healthy subjects, are ultimately considered to be linked to various diseases. Because lipid peroxidation mechanisms (i.e., radical, singlet oxygen, and enzymatic oxidation) can be suppressed by certain proper antioxidants (e.g., radical oxidation is efficiently suppressed by tocopherol), in order to suppress lipid peroxidation successfully, the determination of the peroxidation mechanism involved in the formation of LOOH is deemed crucial. In this study, to determine the peroxidation mechanisms of plasma lipoproteins of healthy subjects, we develop novel analytical methods using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine hydroperoxide (PC 16:0/18:2;OOH) and cholesteryl linoleate hydroperoxide (CE 18:2;OOH) isomers. Using the newly developed methods, these PC 16:0/18:2;OOH and CE 18:2;OOH isomers in the low-density lipoprotein (LDL) and high-density lipoprotein (HDL) of healthy subjects are analyzed. Consequently, it is found that predominant PC 16:0/18:2;OOH and CE 18:2;OOH isomers in LDL and HDL are PC 16:0/18:2;9OOH, PC 16:0/18:2;13OOH, CE 18:2;9OOH, and CE 18:2;13OOH, which means that PC and CE in LDL and HDL are mainly oxidized by radical and/or enzymatic oxidation. In conclusion, the insights about the oxidation mechanisms shown in this study would be useful for a more effective suppression of oxidative stress in the human organism.

Structural Analysis of Lipid Hydroperoxides Using Mass Spectrometry with Alkali Metals

Lipid oxidation is involved in various biological phenomena (e.g., oxylipin generation and oxidative stress). Of oxidized lipid structures, the hydroperoxyl group position of lipid hydroperoxides (LOOHs) is a critical factor in determining their biological roles. Despite such interest, current methods to determine hydroperoxyl group positions possess some drawbacks such as selectivity. While we previously reported mass spectrometric methods using Na⁺ for the highly selective determination of hydroperoxyl group positions, nothing was known except for the fact that sodiated LOOHs (mainly linoleate) provide specific fragment ions. Thus, this study was aimed to investigate the effects of different alkali metals on the fragmentation of LOOHs, assuming its further application to analysis of other complex LOOHs. From the analysis of PC 16:0/18:2;OOH (phosphatidylcholine) and FA 18:2;OOH (fatty acid), we found that fragmentation pathways and ion intensities largely depend on the binding position and type of alkali metals (i.e., Li⁺, Hock fragmentation; Na⁺ and K⁺, α-cleavage (Na⁺ > K⁺); Rb⁺ and Cs⁺, no fragmentation). Furthermore, we proved that this method can be applied to determine the hydroperoxyl group position of esterified lipids (e.g., phospholipids and cholesterol esters) as well as polyunsaturated fatty acids (PUFAs) including n-3, n-6, and n-9 FA. We anticipate that the insights described in this study provide additional unique insights to conventional lipid oxidation research.

Structural changes of ethanolamine plasmalogen during intestinal absorption

Considerable attention has been paid to the absorption mechanisms of plasmalogen (Pls) because its intake has been expected to have preventive effects on brain-related diseases. Possible structural changes of Pls during absorption (i.e., preferential arachidonic acid re-esterification at the sn-2 position and base conversion of ethanolamine Pls (PE-Pls) into choline Pls (PC-Pls)) have previously been proposed. Since the physiological functions of Pls differ according to its structure, further elucidation of such structural changes during absorption is important to understand how Pls exerts its physiological effects in vivo. Hence, the absorption mechanism of Pls was investigated using the lymph-cannulation method and the everted jejunal sac model, with a focus on Pls molecular species. In the lymph-cannulation method, relatively high amounts of PE-Pls 18:0/20:4 and PC-Pls 18:0/20:4 were detected from the lymph even though these species were minor in the administered emulsion. Moreover, a significant increase of PE-Pls 18:0/20:4 and PC-Pls 18:0/20:4 in the intestinal mucosa was also confirmed by the everted jejunal sac model. Therefore, structural changes of PE-Pls in the intestinal mucosa were strongly suggested. The results of this study may provide an understanding of the relationship between intestinal absorption of Pls and exertion of its physiological functions in vivo.

Lipid hydroperoxides in nutrition, health, and diseases

Research on lipid peroxidation in food degradation, oil and fat nutrition, and age-related diseases has gained significant international attention for the view of improvement of societal health and longevity. In order to promote basic studies on these topics, a chemiluminescence detection-high performance liquid chromatography instrument using a high-sensitivity single photon counter as a detector was developed. This instrument enabled us to selectively detect and quantify lipid hydroperoxides, a primary product of lipid peroxidation reactions, as hydroperoxide groups at the lipid class level. Furthermore, an analytical method using liquid chromatography-tandem mass spectrometry has been established to discriminate the position and stereoisomerization of hydroperoxide groups in lipid hydroperoxides. Using these two methods, the reaction mechanisms of lipid peroxidation in food and in the body have been confirmed.

Direct Separation of the Diastereomers of Cholesterol Ester Hydroperoxide Using LC-MS/MS to Evaluate Enzymatic Lipid Oxidation

Cholesterol ester hydroperoxide (CEOOH) is one of the main lipid oxidation products contained in oxidized low-density lipoprotein (LDL). Previous studies suggest that CEOOH in oxidized LDL is closely related to several diseases. Of the oxidation mechanisms of cholesterol ester (CE) in vivo, it has been suggested that enzymatic oxidation induced by lipoxygenase (LOX) plays an important role. Thus, we attempted to develop a method that can evaluate the enzymatic oxidation of CE via the diastereoselective separation of CEOOH bearing 13RS-9Z,11E-hydroperoxy-octadecadienoic acid (13(RS)-HPODE CE). Firstly, we synthesized the standard of 13(RS)-HPODE CE. Using this standard, the screening of analytical conditions (i.e., column, mobile phase, and column temperature) was conducted, and separation of the diastereomers of 13(RS)-HPODE CE was achieved. The diastereoselective separation of 13(RS)-HPODE CE was also confirmed by LC-MS/MS. The developed method (column, CHIRALPAK IB N-3; mobile phase, hexane:ethanol (100:1, v/v); column temperature, 0 °C) can distinguish between enzymatic oxidation and other oxidation mechanisms of CE. Thus, the method can be expected to provide a greater understanding of the biochemical oxidation mechanisms in vivo. Such information will be essential to further elucidate the involvement of CEOOH in various diseases.

Selective covalent targeting of GPX4 using masked nitrile-oxide electrophiles

We recently described glutathione peroxidase 4 (GPX4) as a promising target for killing therapy-resistant cancer cells via ferroptosis. The onset of therapy resistance by multiple types of treatment results in a stable cell state marked by high levels of polyunsaturated lipids and an acquired dependency on GPX4. Unfortunately, all existing inhibitors of GPX4 act covalently via a reactive alkyl chloride moiety that confers poor selectivity and pharmacokinetic properties. Here, we report our discovery that masked nitrile-oxide electrophiles, which have not been explored previously as covalent cellular probes, undergo remarkable chemical transformations in cells and provide an effective strategy for selective targeting of GPX4. The new GPX4-inhibiting compounds we describe exhibit unexpected proteome-wide selectivity and, in some instances, vastly improved physiochemical and pharmacokinetic properties compared to existing chloroacetamide-based GPX4 inhibitors. These features make them superior tool compounds for biological interrogation of ferroptosis and constitute starting points for development of improved inhibitors of GPX4.

Drugs Repurposed as Antiferroptosis Agents Suppress Organ Damage, Including AKI, by Functioning as Lipid Peroxyl Radical Scavengers

BACKGROUND

Ferroptosis, nonapoptotic cell death mediated by free radical reactions and driven by the oxidative degradation of lipids, is a therapeutic target because of its role in organ damage, including AKI. Ferroptosis-causing radicals that are targeted by ferroptosis suppressors have not been unequivocally identified. Because certain cytochrome P450 substrate drugs can prevent lipid peroxidation via obscure mechanisms, we evaluated their antiferroptotic potential and used them to identify ferroptosis-causing radicals.

METHODS

Using a cell-based assay, we screened cytochrome P450 substrate compounds to identify drugs with antiferroptotic activity and investigated the underlying mechanism. To evaluate radical-scavenging activity, we used electron paramagnetic resonance-spin trapping methods and a fluorescence probe for lipid radicals, NBD-Pen, that we had developed. We then assessed the therapeutic potency of these drugs in mouse models of cisplatin-induced AKI and LPS/galactosamine-induced liver injury.

RESULTS

We identified various US Food and Drug Administration-approved drugs and hormones that have antiferroptotic properties, including rifampicin, promethazine, omeprazole, indole-3-carbinol, carvedilol, propranolol, estradiol, and thyroid hormones. The antiferroptotic drug effects were closely associated with the scavenging of lipid peroxyl radicals but not significantly related to interactions with other radicals. The elevated lipid peroxyl radical levels were associated with ferroptosis onset, and known ferroptosis suppressors, such as ferrostatin-1, also functioned as lipid peroxyl radical scavengers. The drugs exerted antiferroptotic activities in various cell types, including tubules, podocytes, and renal fibroblasts. Moreover, in mice, the drugs ameliorated AKI and liver injury, with suppression of tissue lipid peroxidation and decreased cell death.

CONCLUSIONS

Although elevated lipid peroxyl radical levels can trigger ferroptosis onset, some drugs that scavenge lipid peroxyl radicals can help control ferroptosis-related disorders, including AKI.

Evaluation of lipid oxidation mechanisms in beverages and cosmetics via analysis of lipid hydroperoxide isomers

Understanding of lipid oxidation mechanisms (e.g., auto-oxidation and photo-oxidation) in foods and cosmetics is deemed essential to maintain the quality of such products. In this study, the oxidation mechanisms in foods and cosmetics were evaluated through analysis of linoleic acid hydroperoxide (LAOOH) and linoleic acid ethyl ester hydroperoxide (ELAOOH) isomers. Based on our previous method for analysis of LAOOH isomers, in this study, we developed a new HPLC-MS/MS method that enables analysis of ELAOOH isomers. The HPLC-MS/MS methods to analyze LAOOH and ELOOH isomers were applied to food (liquor) and cosmetic (skin cream) samples. As a result, LAOOH and ELAOOH isomers specific to photo-oxidation, and ELAOOH isomers characteristic to auto-oxidation were detected in some marketed liquor samples, suggesting that lipid oxidation of marketed liquor proceeds by both photo- and auto-oxidation during the manufacturing process and/or sales. In contrast, because only LAOOH and ELAOOH isomers specific to auto-oxidation were detected in skin cream stored under dark at different temperatures (-5 °C-40 °C) for different periods (2-15 months), auto-oxidation was considered to be the major oxidation mechanism in such samples. Therefore, our HPLC-MS/MS methods appear to be powerful tools to elucidate lipid oxidation mechanisms in food and cosmetic products.

Determination of triacylglycerol oxidation mechanisms in canola oil using liquid chromatography-tandem mass spectrometry

Triacylglycerol (TG), the main component of edible oil, is oxidized by thermal- or photo- oxidation to form TG hydroperoxide (TGOOH) as the primary oxidation product. Since TGOOH and its subsequent oxidation products cause not only the deterioration of oil quality but also various toxicities, preventing the oxidation of edible oils is essential. Therefore understanding oxidation mechanisms that cause the formation of TGOOH is necessary. Since isomeric information of lipid hydroperoxide provides insights about oil oxidation mechanisms, we focused on dioleoyl-(hydroperoxy octadecadienoyl)-TG (OO-HpODE-TG) isomers, which are the primary oxidation products of the most abundant TG molecular species (dioleoyl-linoleoyl-TG) in canola oil. To secure highly selective and sensitive analysis, authentic OO-HpODE-TG isomer references (i.e., hydroperoxide positional/geometrical isomers) were synthesized and analyzed with HPLC-MS/MS. With the use of the method, photo- or thermal- oxidized edible oils were analyzed. While dioleoyl-(10-hydroperoxy-8E,12Z-octadecadienoyl)-TG (OO-(10-HpODE)-TG) and dioleoyl-(12-hydroperoxy-9Z,13E-octadecadienoyl)-TG (OO-(12-HpODE)-TG) were characteristically detected in photo-oxidized oils, dioleoyl-(9-hydroperoxy-10E,12E-octadecadienoyl)-TG and dioleoyl-(13-hydroperoxy-9E,11E-octadecadienoyl)-TG were found to increase depending on temperature in thermal-oxidized oils. These results prove that our methods not only evaluate oil oxidation in levels that are unquantifiable with peroxide value, but also allows for the determination of oil oxidation mechanisms. From the analysis of marketed canola oils, photo-oxidized products (i.e., OO-(10-HpODE)-TG and OO-(12-HpODE)-TG) were characteristically accumulated compared to the oil analyzed immediately after production. The method described in this paper is valuable in the understanding of oil and food oxidation mechanisms, and may be applied to the development of preventive methods against food deterioration.

Edible oils become rancid when reacting with oxygen under light or heat, degrading into different products depending on the pathway. Kiyotaka Nakagawa at Tohoku University, Japan, and co-workers used instruments that can separate and identify by weight components in mixtures to study light- and heat-induced oxidation of canola oil. Using authentic samples of possible oxidation products as references, the team found that each process generated two unique species from triacylglycerol, the main ingredient in edible oils. These signature compounds allowed the researchers to reveal that heat-oxidation sped up as temperature increased and that light-oxidized products gradually accumulated in off-the-shelf canola oil after production. This method is more sensitive than conventional protocols and can tell exactly how oils are oxidized, useful for developing techniques for food preservation.

A novel chiral stationary phase LC-MS/MS method to evaluate oxidation mechanisms of edible oils

The elucidation of lipid oxidation mechanisms of food is vital. In certain lipids, characteristic lipid hydroperoxide isomers are formed by different oxidation mechanisms (i.e., photo-oxidation or auto-oxidation). For example, linoleic acid is photo-oxidized to 13-9Z, 11E-hydroperoxyoctadecadienoic acid (HPODE), 12-9Z,13E-HPODE, 10-8E,12Z-HPODE and 9-10E,12Z-HPODE, whereas 13-9Z, 11E-HPODE, 13-9E,11E-HPODE, 9-10E,12Z-HPODE and 9-10E,12E-HPODE are formed by auto-oxidation. Therefore, we considered that oxidation mechanisms could be evaluated by analyzing these characteristic positional and cis/trans lipid hydroperoxide isomers. In this study, we developed a novel chiral stationary phase LC-MS/MS (CSP-LC-MS/MS) method to analyze the positional and cis/trans isomers of HPODE, with the use of a chiral column and sodium ion. Also, as an application of the method, either light-exposed or heated edible oils were treated with lipase to hydrolyze triacylglycerols. The resultant fatty acids including HPODE isomers were analyzed with the developed method. As a result, HPODE isomers characteristic to photo-oxidation were certainly detected in light-exposed edible oils. On the other hand, in heated edible oils, the HPODE isomers characteristic to auto-oxidation were largely increased. Thus, the combination of the developed CSP-LC-MS/MS method with lipase proves to be a powerful tool to evaluate the involvement and mechanisms of lipid oxidation in the process of food deterioration.

A novel chiral stationary phase HPLC-MS/MS method to discriminate between enzymatic oxidation and auto-oxidation of phosphatidylcholine

To elucidate the role of enzymatic lipid peroxidation in disease pathogenesis and in food deterioration, we recently achieved stereoselective analysis of phosphatidylcholine hydroperoxide (PCOOH) possessing 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13(S)-9Z,11E-HPODE) using HPLC-MS/MS with a CHIRALPAK OP (+) column. Because enzymatic oxidation progresses concurrently with auto-oxidation, we need to distinguish them further. Here, we attempted such an analysis. First, we used lipoxygenase, linoleic acid, and lysophosphatidylcholine (LPC) to synthesize the enzymatic oxidation product 13(S)-9Z,11E-HPODE PC, and the auto-oxidation products 13(RS)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC, which were used as standards to test the ability of various columns to separate the enzymatic oxidation product from auto-oxidation products. Separation was achieved by connecting in series two columns with different properties: CHIRALPAK OP (+) and CHIRALPAK IB-3. The CHIRALPAK OP (+) column separated 13(R)-9Z,11E-HPODE PC and 13(S)-9Z,11E-HPODE PC, whereas CHIRALPAK IB-3 enabled separation of 13(S)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC. The results for the analysis of both enzymatically oxidized and auto-oxidized lecithin (an important phospholipid mixture in vivo and in food) indicate that our method would be useful for distinguishing enzymatic oxidation and auto-oxidation reactions. Such information will be invaluable for elucidating the involvement of PCOOH in disease pathogenesis and in food deterioration.