Volatile lipid oxidation products

Chemistry and biochemistry of lipid peroxidation products

Oxidative stress and resulting lipid peroxidation is involved in various and numerous pathological states including inflammation, atherosclerosis, neurodegenerative diseases and cancer. This review is focused on recent advances concerning the formation, metabolism and reactivity towards macromolecules of lipid peroxidation breakdown products, some of which being considered as 'second messengers' of oxidative stress. This review relates also new advances regarding apoptosis induction, survival/proliferation processes and autophagy regulated by 4-hydroxynonenal, a major product of omega-6 fatty acid peroxidation, in relationship with detoxication mechanisms. The use of these lipid peroxidation products as oxidative stress/lipid peroxidation biomarkers is also addressed.

Identification of a lipid peroxidation product as the source of oxidation-specific epitopes recognized by anti-DNA autoantibodies

Lipid peroxidation in tissue and in tissue fractions represents a degradative process, which is the consequence of the production and the propagation of free radical reactions primarily involving membrane polyunsaturated fatty acids, and has been implicated in the pathogenesis of numerous diseases, including systemic lupus erythematosus (SLE). We have found that bovine serum albumin incubated with peroxidized polyunsaturated fatty acids significantly cross-reacted with the sera from MRL-lpr mice, a representative murine model of SLE. To identify the active substances responsible for the generation of autoantigenic epitopes recognized by the SLE sera, we performed the activity-guiding separation of a principal source from 13-hydroperoxy-9Z,11E-octadecadienoic acid and identified 4-oxo-2-nonenal (ONE), a highly reactive aldehyde originating from the peroxidation of ω6 polyunsaturated fatty acids, as the source of the autoantigenic epitopes. When the age-dependent change in the antibody titer against the ONE-modified protein was measured in the sera from MRL-lpr mice and control MRL-MpJ mice, all of the MRL-lpr mice developed an anti-ONE titer, which was comparable with the anti-DNA titer. Strikingly, a subset of the anti-DNA monoclonal antibodies generated from the SLE mice showing recognition specificity toward DNA cross-reacted with the ONE-specific epitopes. Furthermore, these dual-specific antibodies rapidly bound and internalized into living cells. These findings raised the possibility that the enhanced lipid peroxidation followed by the generation of ONE may be involved in the pathogenesis of autoimmune disorders.

Characterization of volatile production during storage of lettuce (Lactuca sativa) seed

The duration that seeds stay vigorous during storage is difficult to predict but critical to seed industry and conservation communities. Production of volatile compounds from lettuce seeds during storage was investigated as a non-invasive and early detection method of seed ageing rates. Over 30 volatile compounds were detected from lettuce seeds during storage at 35 degrees C at water contents ranging from 0.03 to 0.09 g H(2)O g(-1) dw. Both qualitative and quantitative differences in volatile composition were noted as a function of water content, and these differences were apparent before signs of deterioration were visible. Seeds stored at high water content (L >or=0.06 g H(2)O g(-1) dw) emitted molecular species indicative of glycolysis (methanol+ethanol), and evidence of peroxidation was apparent subsequent to viability loss. Seeds containing less water (0.03-0.05 g H(2)O g(-1) dw) produced volatiles indicative of peroxidation and survived longer compared with seeds stored under more humid conditions. Production of glycolysis-related by-products correlated strongly with deterioration rate when measured as a function of water content. This correlation may provide a valuable non-invasive means to predict the duration of the early, asymptomatic stage of seed deterioration.

Quantification of N2-carboxymethyl-2'-deoxyguanosine in calf thymus DNA and cultured human kidney epithelial cells by capillary high-performance liquid chromatography-tandem mass spectrometry coupled with stable isotope dilution method

Glyoxal is generated endogenously from the degradation of glucose and the oxidation of carbohydrates, lipids, and the 2-deoxyribose moieties of DNA. Glyoxal is also widely used in industry and is present in cigarette smoke and food. Glyoxal can conjugate with nucleobases and proteins to give advanced glycation end products. N(2)-Carboxymethyl-2'-deoxyguanosine (N(2)-CMdG) and the cyclic 1,N(2)-glyoxal-dG are the major glyoxal adducts formed in DNA. In this study, we first assessed the stabilities of these two adducts. It turned out that 1,N(2)-glyoxal-dG was very unstable, with more than 70% of the adduct being decomposed to dG upon a 24 h incubation at 37 degrees C in phosphate-buffered saline. However, N(2)-CMdG was very stable; less than 0.5% of the lesion was degraded to dG after a 7 day incubation under the same conditions. We further developed a sensitive capillary liquid chromatography-electrospray ionization-tandem mass spectrometry coupled with a stable isotope dilution method and quantified the formation of N(2)-CMdG in calf thymus DNA and 293T human kidney epithelial cells that were exposed to glyoxal and in calf thymus DNA treated with d-glucose. Our results showed that N(2)-CMdG was produced at 2-134 lesions per 10(6) nucleosides in calf thymus DNA when the surrounding glyoxal concentration was increased from 10 to 500 microM and approximately 3-27 lesions per 10(7) nucleosides, while the D-glucose concentration changed from 2 to 50 mM. Furthermore, N(2)-CMdG was induced endogenously in 293T human kidney epithelial cells and exposure to glyoxal further stimulated the formation of this lesion; the level of this adduct ranged from 7 to 15 lesions per 10(8) nucleosides, while the glyoxal concentration increased from 10 microM to 1.25 mM. Collectively, our results suggested that N(2)-CMdG might serve as a biomarker for glyoxal exposure.

Analysis of glyoxal-induced DNA cross-links by capillary liquid chromatography nanospray ionization tandem mass spectrometry

Glyoxal (gx) is an alpha-dicarbonyl species derived endogenously from the metabolism of carbohydrates or nitrosamines and from oxidation of lipids and nucleic acids. It is also widely distributed in foods and the environment. Glyoxal reacts with biomolecules, causing cross-links of proteins and DNA. The cross-linked products of glyoxal with 2'-deoxyribonucleosides have been characterized as dG-gx-dC, dG-gx-dG, and dG-gx-dA. We herein develop a highly specific and sensitive capillary liquid chromatography nanospray ionization tandem mass spectrometry (capLC-NSI/MS/MS) assay for the simultaneous quantification of these three DNA cross-links using a triple-quadrupole mass spectrometer. The sample pretreatment procedures included enzyme hydrolysis of DNA and adduct enrichment by a reversed phase solid phase extraction column. We compared two enzyme hydrolysis conditions, and significantly different adduct levels were observed. This assay achieved attomole sensitivity with detection limits of 12-75 amol injecting each cross-link standard on-column. After calf thymus DNA was incubated with 1.0 mM of glyoxal at 37 degrees C for 30 days, the levels of dG-gx-dC, dG-gx-dG, and dG-gx-dA in this sample were determined as 6.52, 0.80, and 2.74 in 10(5) normal nucleotides, respectively, by capLC-NSI/MS/MS analysis after hydrolysis under optimized conditions. The identity of these cross-links in glyoxal-treated DNA was confirmed by MS(2) and MS(3) scan spectra using a linear ion trap mass spectrometer. In 20 microg of human placental DNA hydrolysate, the levels of dG-gx-dC, dG-gx-dG, and dG-gx-dA were quantified as 2.49, 1.26, and 3.50 in 10(8) normal nucleotides, respectively. These DNA cross-links, if not repaired, can be mutagenic, and they represent a type of damage to the integrity of DNA structure due to exposure of glyoxal.

Maldi-tof mass spectrometry profiling of polar and nonpolar fractions in heated vegetable oils

Triacylglycerol oxidation of thermally stressed (6 h at 180 degrees C, simulating deep-frying conditions) edible vegetable oil (sunflower and olive) was studied using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Chromatographic separation of the nonpolar and polar components from the heated oil performed on silica gel prior to MS analysis significantly enhanced the detection of oxidized components. The spectra contained signals that were assigned to triacylglycerols (TAG), diacylglycerols (DAG), triacylglycerol oxidative dimers, oxidized TAG, and TAG fragments arising from the homolytic beta-scission of linoleyl, peroxy, and alkoxy radicals. Enrichment of the polar compounds prevented mass spectrometric ion suppression, thus allowing the detection of minor species originating from thermal oxidation. In addition, this allowed the monitoring of polar compounds in vegetable oils undergoing mild thermal treatment. As such, chromatographic separation coupled with MALDI-TOF MS analysis provided a rapid, sensitive, and specific tool to assess the thermal oxidation of vegetable oils.

Differential expression levels of aroma-related genes during ripening of apricot (Prunus armeniaca L.)

Fruit aroma is a complex trait, particularly in terms of the number of different biosynthetic pathways involved, the complexity of the final metabolites, and their regulation. In order to understand the underlying biochemical processes involved in apricot aroma, four cDNAs (Pa-aat, EU784138; Pa-adhEU395433; Pa-pdcEU395434; and Pa-loxEU439430) encoding an alcohol acyl transferase (AAT), alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC), and lipoxygenase (LOX), respectively, were isolated and characterized at four stages of maturity in Prunus armeniaca L. cv. Modesto. We observed a reduction in aldehyde and alcohol production between early-harvested fruit and late-harvest fruit, concomitant with an increase in ester production. qPCR analyses showed that the expression levels of the adh gene and the lox gene stayed constant at all stages. Interestingly, aat levels showed a sharp increase in the late-harvest stages concurrent with the changes observed in ester levels. The significance of these changes in relation to aroma production in apricot is discussed.

Influence of time, surface-to-volume ratio, and heating process (continuous or intermittent) on the emission rates of selected carbonyl compounds during thermal oxidation of palm and soybean oils

The aim of this work was to compare the emission rates of selected carbonyl compounds (CC) produced by palm and soybean oils when heated at 180 degrees C in the presence of air, through different time intervals and at different surface-to-volume ratios ( S/ V), in continuous and intermittent processes. The CC were collected and derivatized onto silica C18 cartridges impregnated with an acid 2,4-dinitrophenylhidrazine solution, followed by extraction with acetonitrile and analysis by HPLC-UV and, in some cases, HPLC-MS with electrospray ionization. Among the CC quantified, namely, acetaldehyde, acrolein, propanal, butanal, hexanal, 2-heptenal, and 2-octenal, acrolein was the main emission in both oils and all S/ V ratios, followed by hexanal and 2-heptenal. The soybean oil has presented greater emission rates of acrolein than palm oil. When different S/ V ratios used during the heating process of the oil were compared, the emission rates, in general, were directly related to them, although saturated and nonsaturated CC have had different behaviors toward oxidation reactions. During intermittent heating, there was a trend of increasing emission rates of saturated aldehydes, whereas the opposite was observed with unsaturated aldehydes, probably due to the reactivity of the double bond present in these compounds.

Headspace volatile markers for sensitivity of cocoa (Theobroma cacao L.) somatic embryos to cryopreservation

The mechanisms that reduce the viability of plant somatic embryos following cryopreservation are not known. The objective of the present study was to evaluate the sensitivity of cocoa (Theobroma cacao L.) somatic embryos at different stages of an encapsulation-dehydration protocol using stress-related volatile hydrocarbons as markers of injury and recovery. The plant stress hormone ethylene and volatile hydrocarbons derived from hydroxyl radicals (methane) and lipid peroxidation (ethane) were determined using gas chromatography headspace analysis. Ethylene and methane were the only volatiles detected, with both being produced after each step of the cryogenic protocol. Ethylene production was significantly reduced following exposure to liquid nitrogen, but then increased in parallel with embryo recovery. In contrast, the production of methane was cyclic during recovery, with the first cycle occurring earlier for embryos recovered from liquid nitrogen and desiccation than those recovered from earlier steps in the protocol. These results suggest that loss of somatic embryo viability during cryopreservation may be related to the oxidative status of the tissue, and its capacity to produce ethylene. This study has demonstrated that headspace volatile analysis provides a robust non-destructive analytical approach for assessing the survival and recovery of plant somatic embryos following cryopreservation.

Phenolic molecules in virgin olive oils: a survey of their sensory properties, health effects, antioxidant activity and analytical methods. An overview of the last decade

Among vegetable oils, virgin olive oil (VOO) has nutritional and sensory characteristics that to make it unique and a basic component of the Mediterranean diet. The importance of VOO is mainly attributed both to its high content of oleic acid a balanced contribution quantity of polyunsaturated fatty acids and its richness in phenolic compounds, which act as natural antioxidants and may contribute to the prevention of several human diseases. The polar phenolic compounds of VOO belong to different classes: phenolic acids, phenyl ethyl alcohols, hydroxy-isochromans, flavonoids, lignans and secoiridoids. This latter family of compounds is characteristic of Oleaceae plants and secoiridoids are the main compounds of the phenolic fraction. Many agronomical and technological factors can affect the presence of phenols in VOO. Its shelf life is higher than other vegetable oils, mainly due to the presence of phenolic molecules having a catechol group, such as hydroxytyrosol and its secoiridoid derivatives. Several assays have been used to establish the antioxidant activity of these isolated phenolic compounds. Typical sensory gustative properties of VOO, such as bitterness and pungency, have been attributed to secoiridoid molecules. Considering the importance of the phenolic fraction of VOO, high performance analytical methods have been developed to characterize its complex phenolic pattern. The aim of this review is to realize a survey on phenolic compounds of virgin olive oils bearing in mind their chemical-analytical, healthy and sensory aspects. In particular, starting from the basic studies, the results of researches developed in the last ten years will be focused.

A Probiotic, Lactobacillus fermentum ME-3, Has Antioxidative Capacity in Soft Cheese Spreads with Different Fats

Our aim was to develop a prototype of a functional spread cheese containing both a specific probiotic and n-3 fatty acids and to analyze the viability of the probiotic and stability of n-3 fatty acids during 4 wk of shelf life. Lactobacillus fermentum ME-3 (Lf ME-3) isolated from a healthy Estonian child has been shown to have probiotic and antioxidative properties in several recent studies. In the current study this promising bacterial strain was combined with vegetable oils rich in nutritionally important alpha-linolenic acid and with unflavored cheese to obtain soft cheese spreads with different fat contents. Lactobacillus fermentum ME-3 survived well in all cheeses although the viable count did not increase during 4 wk of storage. The fatty acid composition of cheese triacylglycerols remained stable, whereas the profile of volatile compounds changed: hexanal and pentanal disappeared and the proportion of some alcohols increased. The changes in the profile of volatile compounds show the reductive power of Lf ME-3. A functional spread cheese containing n-3 fatty acids can be prepared with the probiotic Lactobacillus fermentum ME-3 strain leading to a reduced need for chemical anti-oxidants.

A laser desorption ionization time-of-flight mass spectrometry investigation into triacylglycerols oxidation during thermal stressing of edible oils

Laser desorption ionization time-of-flight mass spectrometry (LDI-TOF MS) was used to characterize olive and sunflower oils before and after thermally assisted oxidation in order to develop a rapid fingerprinting method for oil that contains unchanged and oxidized components. No matrix was used to assist laser desorption, and simplified mass spectra were obtained in the mass range of interest (m/z 500-1000), where triacyl- and diacylglycerol ions were observed. Sample preparation was reduced to dissolving oil in chloroform saturated with NaCl. Sodiated triacylglycerols (TAGs), their epoxy/hydroxy and hydroperoxy derivatives, as well as TAGs with shortened chain fatty acids (beta-scission products) were clearly observed in the spectra. LDI-TOF MS rapidly provides semiquantitative information about the oxidation level of edible oil, and thus represents a very useful quality control tool.

The combined effects of α-tocopheryl acetate supplementation and enrofloxacin administration on oxidative stability of turkey meat

1. The combined effects of dietary supplementation of vitamin E and enrofloxacin administration on the oxidative stability of turkey meat were assessed. 2. Enrofloxacin concentrations found in muscles and liver samples from turkeys receiving 200 g/kg of alpha-tocopheryl acetate plus 50 mg/kg of enrofloxacin without a withdrawal period were higher than those of samples administered with 50 mg/kg of enrofloxacin alone. Similarly, meat samples from turkeys receiving 50 mg/kg of enrofloxacin with withdrawal plus 200 mg/kg of alpha-tocopheryl acetate showed a significantly lower vitamin E accumulation than meat samples of the treatment with enrofloxacin without withdrawal plus vitamin E. 3. The results indicated an interaction between the antioxidant and the antibiotic in their effects on oxidation susceptibility and the abiotic safety of meat from turkeys fed on supplemented diets. A mutual stabilisation of both compounds by reducing the effects of free radicals or by affecting the absorption of the compounds is suggested.

Detection of cholesteryl ester hydroperoxide isomers using gas chromatography–mass spectrometry combined with thin-layer chromatography blotting

Oxidative modification of low-density lipoprotein (LDL) has been implicated in the pathogenesis of atherosclerosis. During the oxidation of LDL, cholesteryl esters, the major lipid components in LDL, are oxidized to cholesteryl ester hydroperoxides (CEOOH). The isomers of CEOOH may reflect the reactive species that initiate the peroxidation reaction. In the current study, a novel analytical method for the determination of CEOOH isomers, especially cholesteryl linoleate hydroperoxide isomers, was developed using the combination of two chromatographic techniques: (i) thin-layer chromatography blotting with diphenyl-1-pyrenylphosphine (DPPP) fluorescent detection (DPPP-TLC blotting) and (ii) gas chromatography-electron ionization-mass spectrometry (GC-EI-MS). CEOOH was applied to DPPP-TLC blotting, the obtained DPPP-derived fluorescent spots containing cholesteryl ester hydroxides were extracted and derivatized (hydrogenation, transmethylation, and trimethylsilylation), and the formed methyl ester/trimethylsilylether derivatives of hydroxyoctadecenoic acid were then analyzed by GC-EI-MS. The CEOOH isomers were determined by selected ion monitoring of isomer-specific fragment ions originated from the alpha-cleavage of the trimethylsilyloxyl group. Using these two chromatographic techniques, we were able to detect isomeric CEOOH in the oxidized human LDL. Our results indicated that GC-EI-MS analysis combined with DPPP-TLC blot is a specific method for analyzing cholesteryl ester hydroperoxide isomers in biological samples such as oxidized LDL.

Cryopreservation of shoot tips and meristems

Shoot-tip meristem cryopreservation methodologies are reported for the complementary cryoprotective strategies of vitrification and equilibrium freezing using traditional controlled-rate freezing and chemical additive cryoprotection. Pregrowth, pretreatment, and cold acclimation approaches for the improvement of tolerance to liquid nitrogen are also presented. The chapter concludes by reporting an analytical protocol that profiles volatile hydrocarbon stress markers (for ethylene, hydroxyl radicals, and lipid peroxidation products) during cryopreservation. This method uses noninvasive headspace sampling and gas chromatography, and it is widely applicable across cryogenic systems.