Identification of 1-palmitoyl-2-linoleoyl-phosphatidylethanolamine modifications under oxidative stress conditions by LC-MS/MS

Utilization of LC-MS/MS and Drift Tube Ion Mobility for Characterizing Intact Oxidized Arachidonate-Containing Glycerophosphatidylethanolamine

Lipid peroxidation is a key component in the pathogenesis of numerous disease states, where the oxidative damage of lipids frequently leads to membrane dysfunction and subsequent cellular death. Glycerophosphoethanolamine (PE) is the second most abundant phospholipid found in cellular membranes and, when oxidized, has been identified as an executor of ferroptotic cell death. PE commonly exists in the plasmalogen form, where the presence of the vinyl ether bond and its enrichment in polyunsaturated fatty acids make it especially susceptible to oxidative degradation. This results in a multitude of oxidized products complicating identification and often requiring several analytical techniques for interpretation. In the present study, we outline an analytical approach for the structural characterization of intact oxidized products of arachidonate-containing diacyl and plasmalogen PE. Intact oxidized PE structures, including structural and positional isomers, were identified using complementary liquid chromatography techniques, drift tube ion mobility, and high-resolution tandem mass spectrometry. This work establishes a comprehensive method for the analysis of intact lipid peroxidation products and provides an important pathway to investigate how lipid peroxidation initially impacts glycerophospholipids and their role in redox biology.

Mass Spectrometry Analysis Reveals Lipids Induced by Oxidative Stress in Candida albicans Extracellular Vesicles

Candida albicans is a commensal fungus in healthy humans that causes infection in immunocompromised individuals through the secretion of several virulence factors. The successful establishment of infection is owing to elaborate strategies to cope with defensive molecules secreted by the host, including responses toward oxidative stress. Extracellular vesicle (EV) release is considered an alternative to the biomolecule secretory mechanism that favors fungal interactions with the host cells. During candidiasis establishment, the host environment becomes oxidative, and it impacts EV release and cargo. To simulate the host oxidative environment, we added menadione (an oxidative stress inducer) to the culture medium, and we explored C. albicans EV metabolites by metabolomics analysis. This study characterized lipidic molecules transported to an extracellular milieu by C. albicans after menadione exposure. Through Liquid Chromatography coupled with Mass Spectrometry (LC-MS) analyses, we identified biomolecules transported by EVs and supernatant. The identified molecules are related to several biological processes, such as glycerophospholipid and sphingolipid pathways, which may act at different levels by tuning compound production in accordance with cell requirements that favor a myriad of adaptive responses. Taken together, our results provide new insights into the role of EVs in fungal biology and host-pathogen interactions.

The Effect of Cosmetic Ingredients of Phenol Type on Immediate Pigment Darkening and Their (Photo)Protective Action in Association with Melanin Pigmentation: A Model In Vitro Study

Immediate pigment darkening, the first response of skin to solar exposure leading to undesired irregular pigmentation and dark spots, is the rapid onset of melanin pigmentation resulting from oxidation of the melanogenic indoles, namely 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) available in epidermal melanocytes. The search for effective sunscreen formulations is nowadays focused on UVA/B filters and additional ingredients that may scavenge the reactive oxygen species generated in these processes. In this work the effects of phenolic cosmetic ingredients (CIs), paradol-6, a ginger CO2 extract, and phenylethyl resorcinol on photosensitized DHI and DHICA oxidation were investigated showing a decrease of their consumption and melanin formation (25–30% decrease with phenylethyl resorcinol). The photoprotective role of CIs was also evaluated in model systems. Paradol-6 and ginger CO2 extract can halve linoleic acid peroxidation in the riboflavin-sensitized reaction, while dienes generation reduction (30% of control) was observed in the Rose-Bengal-sensitized photooxidation with paradol-6. The presence of DHI/DHICA melanin exerted a synergistic effect. The decay of thymine free or as a DNA base was almost completely inhibited by CIs. These results open new perspectives in the design of skin care formulations for ameliorating skin spots and contrasting ageing processes associated with sun exposure.

Influence of mixture of spices on phospholipid molecules during water-boiled salted duck processing based on shotgun lipidomics

This study aimed to evaluate the influence of spices on individual phospholipid molecules of water-boiled salted duck (WSD) processing. Shotgun lipidomics was used to determine the structure of individual phospholipid molecules in raw duck meat and changes of phospholipids in processed-WSD with or without spices. A total of 118 phospholipid molecules were determined during the whole processing. Spices had a significant effect on the changes of most individual phospholipid molecules during the processing, but the overall effect on the phospholipid profile was not obvious. Nine phospholipid molecule markers were screened by partial least squares discriminant analysis, which can be used to distinguish with or without spice treatment. The effect of spices on most phospholipid molecules began on the first day of dry-ripening, and gradually became more obvious in the subsequent processing. Spice's main function was to delay the degradation of individual phospholipid molecules.

Characterization of Non-volatile Oxidation Products Formed from Triolein in a Model Study at Frying Temperature

Frying allows cooking food while promoting their organoleptic properties, imparting crunchiness and flavor. The drawback is the oxidation of triacylglycerides (TAGs), leading to the formation of primary oxidized TAGs. Although they have been associated with chronic and degenerative diseases, they are precursors of pleasant flavors in fried foods. Nevertheless, there is a lack of knowledge about the oxidation species present in foods and their involvement in positive/negative health effects. In this work, high-resolution (HR) C₃₀ reversed-phase (RP)-liquid chromatography (LC)-tandem HR mass spectrometry (MS/MS) was used to identify primary oxidation TAGs resulting from heating triolein (160 °C, 5 min). This allows simulating the initial heating process of frying oils usually used to prepare fried foods, such as chips, crisps, and snacks. Beyond hydroxy, dihydroxy, hydroperoxy, and hydroxy-hydroperoxy derivatives, already reported in phospholipids oxidized by Fenton reaction, new compounds were identified, such as dihydroxy-hydroperoxy-triolein derivatives and positional isomers (9/10- and 9/12-dihydroxy-triolein derivatives). These compounds should be considered when proposing flavor formation pathways and/or mitigating lipid-derived reactive oxygen species occurring during food frying.

Lipid peroxidation derived reactive carbonyl species in free and conjugated forms as an index of lipid peroxidation: limits and perspectives

Reactive carbonyl species (RCS) formed by lipidperoxidation as free forms or as enzymatic and non-enzymatic conjugates are widely used as an index of oxidative stress. Besides general measurements based on derivatizing reactions, more selective and sensitive MS based analyses have been proposed in the last decade. Untargeted and targeted methods for the measurement of free RCS and adducts have been described and their applications to in vitro and ex vivo samples have permitted the identification of many biological targets, reaction mechanisms and adducted moieties with a particular relevance to RCS protein adducts. The growing interest in protein carbonylation can be explained by considering that protein adducts are now recognized as being involved in the damaging action of oxidative stress so that their measurement is performed not only to obtain an index of lipid peroxidation but also to gain a deeper insight into the molecular mechanisms of oxidative stress. The aim of the review is to discuss the most novel analytical approaches and their application for profiling reactive carbonyl species and their enzymatic and non-enzymatic metabolites as an index of lipid-oxidation and oxidative stress. Limits and perspectives will be discussed.

Analysis of oxidised and glycated aminophospholipids: Complete structural characterisation by C30 liquid chromatography-high resolution tandem mass spectrometry

The aminophospholipids (APL), phosphatidylethanolamine (PE) and phosphatidylserine (PS) are widely present in cell membranes and lipoproteins. Glucose and reactive oxygen species (ROS), such as the hydroxyl radical (^•OH), can react with APL leading to an array of oxidised, glycated and glycoxidised derivatives. Modified APL have been implicated in inflammatory diseases and diabetes, and were identified as signalling molecules regulating cell death. However, the biological relevance of these molecules has not been completely established, since they are present in very low amounts, and new sensitive methodologies are needed to detect them in biological systems. Few studies have focused on the characterisation of APL modifications using liquid chromatography-tandem mass spectrometry (LC-MS/MS), mainly using C5 or C18 reversed phase (RP) columns. In the present study, we propose a new analytical approach for the characterisation of complex mixtures of oxidised, glycated and glycoxidised PE and PS. This LC approach was based on a reversed-phase C30 column combined with high-resolution MS, and higher energy C-trap dissociation (HCD) MS/MS. C30 RP-LC separated short and long fatty acyl oxidation products, along with glycoxidised APL bearing oxidative modifications on the glucose moiety and the fatty acyl chains. Functional isomers (e.g. hydroxy-hydroperoxy-APL and tri-hydroxy-APL) and positional isomers (e.g. 9-hydroxy-APL and 13-hydroxy-APL) were also discriminated by the method. HCD fragmentation patterns allowed unequivocal structural characterisation of the modified APL, and are translatable into targeted MS/MS fingerprinting of the modified derivatives in biological samples.

Mass spectrometry strategies to unveil modified aminophospholipids of biological interest

The biological functions of modified aminophospholipids (APL) have become a topic of interest during the last two decades, and distinct roles have been found for these biomolecules in both physiological and pathological contexts. Modifications of APL include oxidation, glycation, and adduction to electrophilic aldehydes, altogether contributing to a high structural variability of modified APL. An outstanding technique used in this challenging field is mass spectrometry (MS). MS has been widely used to unveil modified APL of biological interest, mainly when associated with soft ionization methods (electrospray and matrix-assisted laser desorption ionization) and coupled with separation techniques as liquid chromatography. This review summarizes the biological roles and the chemical mechanisms underlying APL modifications, and comprehensively reviews the current MS-based knowledge that has been gathered until now for their analysis. The interpretation of the MS data obtained by in vitro-identification studies is explained in detail. The perspective of an analytical detection of modified APL in clinical samples is explored, highlighting the fundamental role of MS in unveiling APL modifications and their relevance in pathophysiology.

Markers of lipid oxidative damage among office workers exposed intermittently to air pollutants including nanoTiO2 particles

Nanoscale titanium dioxide (nanoTiO2) is a commercially important nanomaterial used in numerous applications. Experimental studies with nanotitania have documented lung injury and inflammation, oxidative stress, and genotoxicity. Production workers in TiO2 manufacturing with a high proportion of nanoparticles and a mixture of other air pollutants, such as gases and organic aerosols, had increased markers of oxidative stress, including DNA and protein damage, as well as lipid peroxidation in their exhaled breath condensate (EBC) compared to unexposed controls. Office workers were observed to get intermittent exposures to nanoTiO2 during their process monitoring. The aim of this study was to investigate the impact of such short-term exposures on the markers of health effects in office workers relative to production workers from the same factory. Twenty-two office employees were examined. They were occupationally exposed to (nano)TiO2 aerosol during their daily visits of the production area for an average of 14±9 min/day. Median particle number concentration in office workers while in the production area was 2.32×104/cm3. About 80% of the particles were <100 nm in diameter. A panel of biomarkers of lipid oxidation, specifically malondialdehyde (MDA), 4-hydroxy-trans-hexenal (HHE), 4-hydroxy-trans-nonenal (HNE), 8-isoprostaglandin F2α (8-isoprostane), and aldehydes C6-C12, were studied in the EBC and urine of office workers and 14 unexposed controls. Nine markers of lipid oxidation were elevated in the EBC of office employees relative to controls (p<0.05); only 8-isoprostane and C11 were not increased. Significant association was found in the multivariate analysis between their employment in the TiO2 production plant and EBC markers of lipid oxidation. No association was seen with age, lifestyle factors, or environmental air contamination. The EBC markers in office employees reached about 50% of the levels measured in production workers, and the difference between production workers and office employees was highly significant (p<0.001). None of these biomarkers were elevated in urine. The approach presented here seems to be very sensitive and useful for non-invasive monitoring of employees exposed to air pollutants, including gases, organic aerosols, and nanoTiO2, and may prove useful for routine biomonitoring purposes. Among them, aldehydes C6, C8, C9, and C10 appear to be the most sensitive markers of lipid oxidation in similar occupational cohorts. One major challenge with sensitive biomonitoring techniques, however, is their non-specificity and difficulty in interpreting the meaning of their physiological values in the context of chronic disease development and damage-repair kinetics.

Soybean phosphatidylcholine liposomes as model membranes to study lipid peroxidation photoinduced by pterin

Oxidized pterins, efficient photosensitizers under UVA irradiation, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. Soybean phosphatidylcholine (SoyPC) liposomes were employed as model membranes to investigate if pterin (Ptr), the parent compound of oxidized pterins, is able to photoinduced lipid peroxidation. Size exclusion chromatography and dialysis experiments showed that Ptr is not encapsulated inside the liposomes and the lipid membrane is permeable to this compound. The formation of conjugated dienes and trienes, upon UVA irradiation, was followed by absorption at 234 and 270 nm, respectively. The photoproducts were characterized by mass spectrometry and oxygenation of SoyPC was demonstrated. In addition, analysis of MS/MS spectra suggested the formation hydroperoxides. Finally, the biological implications of the findings are discussed.

Evaluation of the photooxidation of galactosyl- and lactosylceramide by electrospray ionization mass spectrometry

RATIONALE

Glycosphingolipids are important lipid molecules namely as constituents of the plasma membrane organized in lipid rafts, in signal transduction, and cell-cell communication. Although many human diseases are associated with oxidative stress and lipid oxidation, a link between oxidative stress and modification of glycosphingolipids has never been addressed.

METHODS

In this study, the structural changes caused by UVA-induced photooxidation of galactosyl- (GalCer) and lactosylceramide (LacCer) molecular species were studied by electrospray ionization mass spectrometry (ESI-MS and MS/MS), using a quadrupole time-of-flight (QTOF) mass spectrometer and high-performance liquid chromatography/tandem mass spectrometry with a C5 stationary phase (C5 HPLC/MS/MS) using a linear ion trap.

RESULTS

ESI-MS spectra of GalCer and LacCer after photooxidation showed new ions with a mass shift of +32 Da when compared with the ions of the non-modified glycosphingolipids. These new species were assigned as hydroperoxyl derivatives, confirmed by HPLC/MS/MS and through FOX 2 assay. In the ESI-MS and LC/MS of lactosylceramide a new ion with lower m/z value, assigned as glucosylceramide (GlcCer) + 32 Da, was also detected and proposed to be formed due to oxidative cleavage of lactosyl moieties. ESI-MS/MS of the oxidized species allowed us to infer the presence of isomeric hydroperoxyl derivatives, with the hydroperoxyl moiety either linked to the sphingosine backbone or in the unsaturated acyl chain. Oxidation in the sugar moieties was observed in the case of LacCer, suggesting an oxidation via radical reactive oxygen species that can induce the oxidative cleavage of the lactosyl moiety.

CONCLUSIONS

This study shows that glycosphingolipids are prone to oxidation and the identified mass spectrometry fingerprint of oxidized galactosyl- and lactosylceramide species will support their future identification in lipidomic studies of biological samples under oxidative conditions.

Development of a direct in-matrix extraction (DIME) protocol for MALDI-TOF-MS detection of glycated phospholipids in heat-treated food samples

In foodstuffs, one of the main factors inducing modifications in phospholipids (PLs) structure is the heat treatment. Among PLs, only phosphatidylethanolamines and phosphatidylserines, due to their free amino group, can be involved in Maillard reaction and can form adducts with reducing sugars, besides other by-products called advanced glycation end-products. To date, glycated lipid products are less characterized in comparison to proteins. The aim of this work was to develop a novel, rapid and sensitive extraction protocol for the detection and characterization of modified PLs (glycated and oxidized) by means of matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). At first, to investigate the formation of glycated and/or short chain by-products in different classes of PLs, representative standards were heated with or without sugar (lactose or glucose) and subjected to traditional lipid extraction methods as Bligh and Dyer and to the novel direct in matrix extraction (DIME) using 1,8-bis(dimethylamino)naphthalene as preconcentrating matrix. MALDI-MS analysis in negative ion mode allowed detecting glycation and oxidation products both on fatty acid and glucose moieties. Then, the procedure was successfully applied to different heat-treated and powdered samples (milk powders, pasteurized milk, ultra-high-temperature milk and soy flour) for the detection of modified PLs in complex foods. The currently developed DIME protocol could be a powerful tool for understanding lipid glycation also in biological samples.

Photosensitized oxidation of phosphatidylethanolamines monitored by electrospray tandem mass spectrometry

Photodynamic therapy combines visible light and a photosensitizer (PS) in the presence of molecular oxygen to generate reactive oxygen species able to modify biological structures such as phospholipids. Phosphatidylethanolamines (PEs), being major phospholipid constituents of mammalian cells and membranes of Gram-negative bacteria, are potential targets of photosensitization. In this work, the oxidative modifications induced by white light in combination with cationic porphyrins (Tri-Py(+)-Me-PF and Tetra-Py(+)-Me) were evaluated on PE standards. Electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) were used to identify and characterize the oxidative modifications induced in PEs (POPE: PE 16:0/18:1, PLPE: PE 16:0/18:2, PAPE: PE 16:0/20:4). Photo-oxidation products of POPE, PLPE and PAPE as hydroxy, hydroperoxy and keteno derivatives and products due to oxidation in ethanolamine polar head were identified. Hydroperoxy-PEs were found to be the major photo-oxidation products. Quantification of hydroperoxides (PE-OOH) allowed differentiating the potential effect in photodamage of the two porphyrins. The highest amounts of PE-OOH were notorious in the presence of Tri-Py(+)-Me-PF, a highly efficient PS against bacteria. The identification of these modifications in PEs is an important key point in the understanding cell damage processes underlying photodynamic therapy approaches.

Characterization of phosphatidylcholine oxidation products by MALDI MS(n)

Phospholipid oxidation has been implicated in the pathogenesis and progression of numerous age-related and neurodegenerative diseases. Despite these implications, this broad class of biomolecules remains poorly characterized. In this work, the fragmentation patterns of [M + H](+) and [M + Na](+) ions of intact phosphatidylcholine oxidation products (OxPCs) were characterized by matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI MS(n), n = 2, 3, and 4). MS(2) of both the [M + H](+) and [M + Na](+) ions of short-chain OxPCs yielded product ions related to the PC headgroup and the fatty acid substituents. MS(3) of the [M + Na - N(CH3)3](+) ions yielded fragmentation indicative of the OxPC modification; specifically, a product ion corresponding to the neutral loss of CO2 (NL of 44) was observed for OxPCs containing a terminal carboxylic acid rather than an aldehyde. Furthermore, MS(4) of the [M + Na - HPO4(CH2)2N(CH3)3](+) ions resulted in fragmentation pathways dependent on the sn-2 fatty acid chain length and type of functional group(s). Specifically, CHO-containing OxPCs with palmitic acid esterified to the sn-1 position of the glycerol backbone yielded a NL of 254, 2 u less than the nominal mass of palmitic acid, whereas the analogous terminal COOH-containing OxPCs demonstrated a NL of 256. Finally, the presence of a γ-ketone relative to the terminal carboxyl group resulted in C-C bond cleavages along the sn-2 substituent, providing diagnostic product ions for keto-containing OxPCs. This work illustrates the enhanced selectivity afforded by MS(n) on the linear ion trap and develops a method for the identification of individual products of PC oxidation.

Modified phosphatidylethanolamines induce different levels of cytokine expression in monocytes and dendritic cells

Glycation of phosphatidylethanolamine (PE) is a reaction that is known to occur under the chronic hyperglycemic conditions found in diabetes. Glycated phosphatidylethanolamines were found in plasma and atherosclerotic plaques of diabetic patients, and its presence was correlated with increased oxidative stress. Moreover, upregulation of cytokines and other inflammatory mediators can be observed not only in diabetes, but also under oxidized phosphatidylcholine stimulation. In this study, we evaluate the effect of dipalmitoyl-phosphatidylethanolamine (DPPE) and linoleoyl-palmitoyl-phosphatidylethanolamine (PLPE) structural oxidation, glycation and glycoxidation, on monocyte and myeloid dendritic cell stimulation. Expression of cytokines, IL-1β, IL-6, IL-8, MIP-1β and TNF-α, were determined using flow cytometry after cell stimulations with native PEs, oxidized, glycated and glycoxidized PEs. Native PE, PLPE and DPPE, and all modified PEs were able to increase the stimulation levels of monocytes and mDCs. Generally, in monocytes and mDCs stimulation, GluOxPLPE and GluDPPE were the PLPE/DPPE modifications that induced the most pronounced rise in cytokine production. However, GluOxDPPE was the DPPE modification that produced the lowest stimulation levels of mDCs and monocytes. Our results indicate that glycated PE and glycoxidized PE may have an important contribution to the low-grade systemic inflammation associated with diabetes and to the development of diabetic complications.

Photooxidation of glycated and non-glycated phosphatidylethanolamines monitored by mass spectrometry

Phosphatidylethanolamines (PE) are one of the major components of cells membranes, namely in skin and in retina, that are continuously exposed to solar UV radiation being major targets of photooxidation damage. In addition, due to the presence of the free amine group, PE can also undergo glycation, in hyperglycemic conditions which may increase the susceptibility to oxidation. The aim of this study is to develop a model, based on mass spectrometry (MS) analysis, to identify photooxidative degradation of selected PE (POPE: PE 16:0/18:1, PLPE: PE 16:0/18:2, PAPE: PE 16:0/20:4) and glycated PEs due to UV irradiation. Photooxidation products were analysed by electrospray ionization MS (ESI-MS) and tandem MS (ESI-MS/MS) in positive and negative mode. Emphasis is placed in the influence of glycation in the generation of distinct photooxidation products. ESI-MS spectra of PE after UV photo-irradiation showed mainly hydroperoxy derivatives, due to oxidation of unsaturated fatty acyl chains. Glycated PE gave rise to several new photooxidation products formed due to oxidative cleavages of the glucose moiety, namely between C1 and C2, C2 and C3, and C5 and C6 of this sugar unit. These new products were identified by ESI-MS/MS in positive mode showing distinct neutral loss depending on the different structure of the polar head group. These new identified advanced glycated photooxidation products may have a deleterious role in the etiology of diabetic retinopathy and in diabetic retinal microvascular complications.

Identification of free radicals in oxidized and glycoxidized phosphatidylethanolamines by spin trapping combined with tandem mass spectrometry

RATIONALE

Nonenzymatic glycation of phosphatidylethanolamines (PEs) seems to a have a role in angiogenesis and atherosclerosis. Glycated PEs are more easily oxidized, enhancing oxidative stress. This study aims to evaluate the influence of glycation on the formation of intermediate radical species during oxidation of glycated PEs.

METHODS

In the present study, the radical intermediaries formed during the oxidation of palmitoyl-lineoyl phosphatidylethanolamine (PLPE) and glycated PLPE (gPLPE) were trapped using a spin trap (DMPO) and the radical adducts were analyzed by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Mass spectra were acquired using a electrospray Q-TOF 2 mass spectrometer.

RESULTS

Several spin adducts of PLPE and gPLPE were identified, corresponding to carbon- and oxygen-centered radicals. Interpretation of the MS/MS spectra showed the existence of different sites where radical formation occurred, at the sn-2 acyl chain, ethanolamine moiety (particularly in C-1) and, in the case of glycated derivatives, also in the glucose moiety (particularly in C-3, C-4 and C-5).

CONCLUSIONS

These results suggested the presence of more sites susceptible to oxidation in glycated PLPE, which may be responsible for the increase in the oxidative reaction rate occurring in glycated compounds.

A simplified procedure for semi-targeted lipidomic analysis of oxidized phosphatidylcholines induced by UVA irradiation

Oxidized phospholipids (OxPLs) are increasingly recognized as signaling mediators that are not only markers of oxidative stress but are also "makers" of pathology relevant to disease pathogenesis. Understanding the biological role of individual molecular species of OxPLs requires the knowledge of their concentration kinetics in cells and tissues. In this work, we describe a straightforward "fingerprinting" procedure for analysis of a broad spectrum of molecular species generated by oxidation of the four most abundant species of polyunsaturated phosphatidylcholines (OxPCs). The approach is based on liquid-liquid extraction followed by reversed-phase HPLC coupled to electrospray ionization MS/MS. More than 500 peaks corresponding in retention properties to polar and oxidized PCs were detected within 8 min at 99 m/z precursor values using a single diagnostic product ion in extracts from human dermal fibroblasts. Two hundred seventeen of these peaks were fluence-dependently and statistically significantly increased upon exposure of cells to UVA irradiation, suggesting that these are genuine oxidized or oxidatively fragmented species. This method of semitargeted lipidomic analysis may serve as a simple first step for characterization of specific "signatures" of OxPCs produced by different types of oxidative stress in order to select the most informative peaks for identification of their molecular structure and biological role.

Structural characterization of oxidized glycerophosphatidylserine: evidence of polar head oxidation

Non-oxidized phosphatidylserine (PS) is known to play a key role in apoptosis but there is considerable research evidence suggesting that oxidized PS also plays a role in this event, leading to the increasing interest in studying PS oxidative modifications. In this work, different PS (1-palmitoyl-2-linoleoyl-sn-glycero-3-phospho-L-serine (PLPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS), and 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS) were oxidized in vitro by hydroxyl radical, generated under Fenton reaction conditions, and the reactions were monitored by ESI-MS in negative mode. Oxidation products were then fractionated by thin layer chromatography (TLC) and characterized by tandem mass spectrometry (MS/MS). This approach allowed the identification of hydroxyl, peroxy, and keto derivatives due to oxidation of unsaturated fatty acyl chains. Oxidation products due to oxidation of serine polar head were also identified. These products, with lower molecular weight than the non-modified PS, were identified as [M - 29 - H](-) (terminal acetic acid), [M - 30 - H](-) (terminal acetamide), [M - 13 - H](-) (terminal hydroperoxyacetaldehyde), and [M - 13 - H](-) (terminal hydroxyacetaldehyde plus hydroxy fatty acyl chain). Phosphatidic acid was also formed in these conditions. These findings confirm the oxidation of the serine polar head induced by the hydroxyl radical. The identification of these modifications may be a valuable tool to evaluate phosphatidylserine alteration under physiopathologic conditions and also to help understand the biological role of phosphatidylserine oxidation in the apoptotic process and other biological functions.

Synergistic effect of high and low molecular weight molecules in the foamability and foam stability of sparkling wines

The foam of sparkling wines is a key parameter of their quality. However, the compounds that are directly involved in foam formation and stabilization are not yet completely established. In this work, seven sparkling wines were produced in Bairrada appellation (Portugal) under different conditions and their foaming properties evaluated using a Mosalux-based device. Fractionation of the sparkling wines into four independent fractions, (1) high molecular weight material, with molecular weight higher than 12 kDa (HMW), (2) hydrophilic material with molecular weigh between 1 and 12 kDa (AqIMW), (3) hydrophobic material with molecular weigh between 1 and 12 kDa (MeIMW), and (4) hydrophobic material with a molecular weight lower than 1 kDa (MeLMW), allowed the observation that the wines presenting the lower foam stability were those that presented lower amounts of the MeLMW fraction. The fraction that presented the best foam stability was HMW. When HMW is combined with MeLMW fraction, the foam stability largely increased. This increase was even larger, approaching the foam stability of the sparkling wine, when HMW was combined with the less hydrophobic subfraction of MeLMW (fraction 3). Electrospray tandem mass spectrometry (ESI-MS/MS) of fraction 3 allowed the assignment of polyethylene glycol oligomers (n = 5-11) and diethylene glycol 8-hydroxytridecanoate glyceryl acetate. To observe if these molecules occur in sparkling wine foam, the MeLMW was recovered directly from the sparkling wine foam and was also analyzed by ESI-MS/MS. The presence of monoacylglycerols of palmitic and stearic acids, as well as four glycerylethylene glycol fatty acid derivatives, was observed. These surface active compounds are preferentially partitioned by the sparkling wine foam rather than the liquid phase, allowing the inference of their role as key components in the promotion and stabilization of sparkling wine foam.

Liquid chromatography/tandem mass spectrometry analysis of long-chain oxidation products of cardiolipin induced by the hydroxyl radical

The anionic phospholipid cardiolipin (CL) is found almost exclusively in the inner membrane of mitochondria, playing an important role in energy metabolism. Oxidation of CL has been associated with apoptotic events and various pathologies. In this study, electrospray ionization mass spectrometry coupled with liquid chromatography (LC/ESI-MS) was used to identify tetralinoleoyl-cardiolipin (TLCL) modifications induced by the OH(·) radical generated under Fenton reaction conditions (H(2)O(2) and Fe(2+)). The identified oxidation products of TLCL contained 2, 4, 6 and 8 additional oxygen atoms. These long-chain oxidation products were characterized by LC/ESI-MS/MS as doubly [M-2H](2-) and singly charged [M-H](-) ions. A detailed analysis of the fragmentation pathways of these precursor ions allowed the identification of hydroperoxy derivatives of CL. MS/MS analysis indicated that CL oxidation products with 4, 6 and 8 oxygen atoms have one fatty acyl chain bearing 4 oxygen atoms ([RCOO+4O](-)). Even when the TLCL molecule was oxidized by the addition of eight oxygen atoms, one of the acyl chains remained non-modified and one fatty acyl chain contained three or four oxygen atoms. This led us to conclude that under oxidative conditions by the OH(·) radical, the distribution of oxygens/peroxy groups in the CL molecule is not random, even when CL has the same fatty acyl chains in all the positions. Using mass spectrometry, the oxidation products have been unequivocally assigned, which may be useful for their detection in biological samples.

Advances in methods for the determination of biologically relevant lipid peroxidation products

Lipid peroxidation is recognized to be an important contributor to many chronic diseases, especially those of an inflammatory pathology. In addition to their value as markers of oxidative damage, lipid peroxidation products have also been shown to have a wide variety of biological and cell signalling effects. In view of this, accurate and sensitive methods for the measurement of lipid peroxidation products are essential. Although some assays have been described for many years, improvements in protocols are continually being reported and, with recent advances in instrumentation and technology, highly specialized and informative techniques are increasingly used. This article gives an overview of the most currently used methods and then addresses the recent advances in some specific approaches. The focus is on analysis of oxysterols, F(2)-isoprostanes and oxidized phospholipids by gas chromatography or liquid chromatography mass spectrometry techniques and immunoassays for the detection of 4-hydroxynonenal.

Oxidation of glycated phosphatidylethanolamines: evidence of oxidation in glycated polar head identified by LC-MS/MS

Phosphatidylethanolamine glycation occurs in diabetic patients and was found to be related with oxidative stress and with diabetic complications. Glycated phosphatidylethanolamines seem to increase oxidation of other molecules; however, the reason why is not understood. In this work, we have studied the oxidation of glycated phosphatidylethanolamines (1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphatidylethanolamine (PLPE) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylethanolamine (dPPE)) using a Fenton system. Liquid chromatography-electrospray ionization (ESI)-mass spectrometry and ESI-tandem mass spectrometry in both positive and negative modes were used for detecting and identifying the oxidation products. We were able to identify several oxidation products with oxidation in unsaturated sn-2 acyl chain of PLPE, as long- and short-chain products with main oxidation sites on C-7, C-8, C-9, and C-12 carbons. Other products were identified in both glycated PLPE and glycated dPPE, revealing that oxidation also occurs in the glycated polar head. This fact has not been reported before. These products may be generated from oxidation of glycated phosphatidylethanolamines (PE) as Schiff base, leading to short-chain product without the amine moiety, due to cleavage of glycated polar head and long-chain product with two keto groups linked to the glycated polar head or from glycated PE as Amadori product, short-chain products with -NHCHO and -NHCHOHCHO terminal in polar head. Oxidation of glycated phosphatidylethanolamines occurred more quickly than the oxidation of non-glycated phosphatidylethanolamines probably because of the existence of more oxidation sites derived from glycation of polar head group. Monitoring glycated polar head oxidation could be important to evaluate oxidative stress modifications that occur in diabetic patients.