Cis-trans isomerization of polyunsaturated fatty acid residues in phospholipids catalyzed by thiyl radicals

A novel tomato pulp with high cis-lycopene content and bioaccessibility through plant-derived sulfur-containing compounds in a simulated food system

Cis (Z)-lycopene exhibits higher bioavailability and tissue accumulation efficiency compared with all-trans (E)-lycopene. A simulated food system was developed to convert all-E-lycopene to its Z-isomers during processing. This system consisted of an aqueous phase containing plant-derived sulfur-containing compounds and a medium-chain triglyceride (MCT) oil phase with dissolved all-E-lycopene. The study aimed to evaluate the effects of sulfur-containing compounds from different plant sources and heat treatments on lycopene isomerization and degradation. The results indicated that, compared with shiitake extract, leek extract, glucoraphanin, wasabi extract, and horseradish, allicin, alliin, and sulforaphane significantly promoted the Z-lycopene content under the optimal heat treatment conditions. The Z-lycopene content increased from 4.91 % to 77.1 %, 68.91 %, and 75.84 % in the allicin, alliin, and sulforaphane groups, respectively. Additionally, except for the shiitake extract group, the addition of other sulfur-containing compounds did not significantly affect lycopene degradation compared with thermal treatment alone (p > 0.05). For better quantitative analysis in food systems, alliin was used as a reference. The application of this method demonstrated that in screened alliin-rich garlic juice (21.20 mg/g) mixed with tomato pulp and MCT oil system, the percentage of total-Z-lycopene increased from 12.14 % to 59.57 %. The bioaccessibility of total-Z-lycopene significantly improved with the addition of garlic juice (p < 0.01). Among all isomers, the bioaccessibility of 9-Z-lycopene and 5-Z-lycopene showed the most significant increase (p < 0.01). This novel tomato pulp system enables the effective utilization of lycopene during processing.

Vegetables containing sulfur compounds promote trans-isomerization of unsaturated fatty acids in triacylglycerols during the cooking process

Growing evidence indicates that the intake of trans-fatty acids (TFAs) has been associated with a higher risk of cardiovascular disease; therefore, various industrial measures have been taken to reduce the amount of TFAs consumed. However, research on TFAs formed during cooking is limited. Isothiocyanates and polysulfides, which are widely distributed in various vegetables, have recently been shown to promote the cis-trans isomerization of double bonds. However, the effects of these sulfur compounds on unsaturated fatty acids (UFAs) comprising edible oils (triacylglycerols) are unknown. To further reduce the intake of TFAs, a better understanding of the effect of the presence of these sulfur compounds on the formation of TFAs under cooking conditions is important. This study investigated the isomerization characteristics of UFAs in the presence of isothiocyanates and polysulfides in model systems using high-purity compounds as well under simulated cooking conditions using food samples. The outcomes of the model system indicated that these sulfur compounds significantly enhance the thermal isomerization, especially at temperatures ≥140 °C. Furthermore, the addition of antioxidants substantially inhibited the isomerization enhancement effect of isothiocyanates, whereas that of polysulfides was marginally moderated. A similar trend was observed under simulated cooking conditions. The results suggest that cooking with sulfur-compound-rich vegetables, especially garlic and onion, which are rich in polysulfides, can potentially result in increased trans fatty acid intake.

Inhibition mechanism of trans-resveratrol on thermally induced trans fatty acids in peanut oil

The unanticipated inhibitory effect of trans-resveratrol (trans-Res) on the formation of trans fatty acids (TFAs) by thermal isomerization of peanut oil (PO) and its mechanism were investigated by experiment and density functional theory. Results showed that trans-Res inhibited the amount and formation rate of TFAs. trans-Res first inhibited the formation of C18:2, then C18:1, by the mechanism of proton transfer isomerism. The most active reaction site of trans-Res (4'-OH free radical) preferentially combined with the OOL-L-C11• (di-allyl) and then with OOL-O-C11• (mono-allyl) allyl groups in PO, resulting in the higher reaction energy barrier of speed control steps in OOL-L (transition state 1) and OOL-O (transition state 2), and the lower reaction rate of OOL-L and OOL-O (both decreased by 1-10³ times), to reduce the formation of TFAs. Our study provided a theoretical foundation for the precise regulation of natural hydroxy compound to TFAs in oil.

Disentangling the Puzzling Regiochemistry of Thiol Addition to o-Quinones

The addition of thiol compounds to o-quinones, as exemplified by the biologically relevant conjugation of cysteine to dopaquinone, displays an anomalous 1,6-type regiochemistry compared to the usual 1,4-nucleophilic addition, for example, by amines, which has so far eluded intensive investigations. By means of an integrated experimental and computational approach, herein, we provide evidence that the addition of glutathione, cysteine, or benzenethiol to 4-methyl-o-benzoquinone, modeling dopaquinone, proceeds by a free radical chain mechanism triggered by the addition of thiyl radicals to the o-quinone. In support of this conclusion, DFT calculations consistently predicted the correct regiochemistry only for the proposed thiyl radical-quinone addition pathway. These results would prompt a revision of the commonly accepted mechanisms for thiol-o-quinone conjugation and stimulate further work aimed at assessing the impact of the free radical processes in biologically relevant thiol–quinone interactions.

Free-Radical-Mediated Formation of Trans-Cardiolipin Isomers, Analytical Approaches for Lipidomics and Consequences of the Structural Organization of Membranes

Free-radical-mediated processes, such as peroxidation, isomerization and hydrogenation affecting fatty acid integrity and biological functions, have a trans-disciplinary relevance. Cardiolipins (CL, (1,3-diphosphatidyl-sn-glycerol)) and tetra-linoleoyl-CL are complex phospholipids, exclusively present in the Inner Mitochondrial Membrane (IMM) lipids, where they maintain membrane integrity and regulate enzyme functionalities. Peroxidation pathways and fatty acid remodeling are known causes of mitochondrial disfunctions and pathologies, including cancer. Free-radical-mediated isomerization with the change of the cis CL into geometrical trans isomers is an unknown process with possible consequences on the supramolecular membrane lipid organization. Here, the formation of mono-trans CL (MT-CL) and other trans CL isomers (T-CL) is reported using CL from bovine heart mitochondria and thiyl radicals generated by UV-photolysis from 2-mercaptoethanol. Analytical approaches for CL isomer separation and identification via ¹H/¹³C NMR are provided, together with the chemical study of CL derivatization to fatty acid methyl esters (FAME), useful for lipidomics and metabolomics research. Kinetics information of the radical chain isomerization process was obtained using γ-irradiation conditions. The CL isomerization affected the structural organization of membranes, as tested by the reduction in unilamellar liposome diameter, and accompanied the well-known process of oxidative consumption induced by Fenton reagents. These results highlight a potential new molecular modification pathway of mitochondrial lipids with wide applications to membrane functions and biological consequences.

Impact of onions in tomato-based sauces on isomerization and bioaccessibility of colorless carotenes: phytoene and phytofluene

Onions as an interesting ingredient have been proved to promote Z-isomerization of lycopene and increase bioaccessibility of total-lycopene. Phytoene (PT) and phytofluene (PTF), the precursors of lycopene, are colorless carotenes, which are attracting much attention and are also abundant in tomatoes. Therefore, onions might also affect the distribution and bioaccessibility of PT and PTF isomers during heating tomato (hot-break and cold-break purees)-onion-extra virgin olive oil (EVOO) sauces. The addition of onions (or diallyl disulfide present in onions) into tomato purees did not cause degradation of PT or PTF; however it favored E/Z-isomerization of PT and PTF by reducing the proportions of their natural Z-isomers (Z-15-PT and Z2,3-PTF) and decreased the bioaccessibility of total-PT and total-PTF. Simultaneously, a complex picture was obtained for the effect of onions on the bioaccessibility of individual PT and PTF isomers, depending on the precise isomer. Bioaccessibility of PT and PTF isomers in tomato-based sauces decreased in the order: 15-Z-PT > all-E-PT; Z2,3-PTF > all-E-PTF > Z4 or Z5-PTF; total-PT > total-PTF. E-isomerization of PT and PTF enhanced by onions during heating tomato-onion purees decreased their bioaccessibility.

Heating tomato puree in the presence of lipids and onion: The impact of onion on lycopene isomerization

Z-lycopene isomers are more bioavailable than all-E-lycopene, especially 5-Z-lycopene. Based on our observations, the addition of unblanched onion could favor Z-isomerization of lycopene (by more than 94%) during heating tomato-onion-extra virgin olive oil (EVOO) purees at 90 °C for 2 h. The increase in Z-lycopene was correlated linearly with the addition of unblanched onion, with R² > 0.92, and increased rates of 5-Z-lycopene were 3-4 times higher than for 9-Z-lycopene and 13-Z-lycopene. Diallyl disulfide (DADS), formed by alliinase-catalyzed breakdown of non-volatile precursors in onion, contributed to these increases and correlated linearly (R² > 0.79, 0-0.50 mg/g puree) with increased Z-lycopene. Increased rates of 5-Z-lycopene were also 3-4 times higher than for 9-Z-lycopene and 13-Z-lycopene. However, blanching of onion, in tomato-onion-EVOO purees, before heating, significantly decreased the effect of onion on Z-isomerization of lycopene.

[Cu(TPMA)(Phen)](ClO4)2: Metallodrug Nanocontainer Delivery and Membrane Lipidomics of a Neuroblastoma Cell Line Coupled with a Liposome Biomimetic Model Focusing on Fatty Acid Reactivity

The use of copper complexes for redox and oxidative-based mechanisms in therapeutic strategies is an important field of multidisciplinary research. Here, a novel Cu(II) complex [Cu(TPMA)(Phen)](ClO4)2 (Cu-TPMA-Phen, where TPMA = tris-(2-pyridylmethyl)amine and Phen = 1,10-phenanthroline) was studied using both the free and encapsulated forms. A hollow pH-sensitive drug-delivery system was synthesized, characterized, and used to encapsulate and release the copper complex, thus allowing for the comparison with the free drug. The human neuroblastoma-derived cell line NB100 was treated with 5 μM Cu-PMA-Phen for 24 h, pointing to the consequences on mono- and polyunsaturated fatty acids (MUFA and PUFA) present in the membrane lipidome, coupled with cell viability and death pathways (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium viability assay, flow cytometry, microscopy, caspase activation). In parallel, the Cu-TPMA-Phen reactivity with the fatty acid moieties of phospholipids was studied using the liposome model to work in a biomimetic environment. The main results concerned: (i) the membrane lipidome in treated cells, involving remodeling with a specific increase of saturated fatty acids (SFAs) and a decrease of MUFA, but not PUFA; (ii) cytotoxic events and lipidome changes did not occur for the encapsulated Cu-TPMA-Phen, showing the influence of such nanocarriers on drug activity; and (iii) the liposome behavior confirmed that MUFA and PUFA fatty acid moieties in membranes are not affected by oxidative and isomerization reactions, proving the different reactivities of thiyl radicals generated from amphiphilic and hydrophilic thiols and Cu-TPMA-Phen. This study gives preliminary but important elements of copper(II) complex reactivity in cellular and biomimetic models, pointing mainly to the effects on membrane reactivity and remodeling based on the balance between SFA and MUFA in cell membranes that are subjects of strong interest for chemotherapeutic activities as well as connected to nutritional strategies.

Radical Arene Addition vs Radical Reduction: Why Organometal Hydride Chain Reactions Stop and How To Make Them Go

Nonideal kinetic chain analysis was used to examine the kinetic limitations of free-radical synthesis. Homolytic aromatic substitution (HAS: ArH + R^• → ArR + H^•) occurs in a chain-terminating side reaction to the tributyltin hydride ( SnH) reduction chain (RX + SnH + ( i^•)_cat. → RH + SnX). Kinetic modeling of premixed and slow reagent addition reactions have clarified the mechanisms of SM HAS, with the azo initiator ( iNN i) acting not only as radical source but also (as an H^• acceptor) as the redox catalyst for aromatization, and/or as a postaddition oxidant. Refractory halides and other hitherto baffling anomalies may arise from the build up of ipso (rather than ortho)-cycloadduct radicals in the steady-state radical population. The implications of these findings for "tin-free" radical chains (and emerging photoredox methods) are considered via historical and recent examples of the effects of chain-degrading radical transfer (to substrate, product, solvent, initiator, and/or reagent ligands) on the reagent's chain.

Why Not Trans? Inhibited Radical Isomerization Cycles and Coupling Chains of Lipids and Alkenes with Alkane -thiols

Reversible addition of thiyl radicals to cis fatty acids converts them into trans fatty acids, L _Z + S^• ⇄ SL^• ⇄ L _E + S^•, in a cycle that, uninterrupted, would rapidly isomerize lipids exposed to radicals and thiols. One reason this does not happen in foods and organisms is because the cycle is interrupted, by exothermic allylic abstraction, L + S^• → L^• + SH. Autoinhibition limits the cis-trans cycle length to around 400-500 (L _E per S^•) in a MUFA model (methyl oleate) and just ∼13-15 in a PUFA lipid model (methyl linoleate). The weak C-H bonds in bisallylic groups in PUFAs thereby act as the first line of defense against thiyl cis-trans cycles in biolipid solutions (±O₂). With the intriguing exception of vitamin E in MUFA, thiyl-active antioxidants inhibit isomerization in much the same way as they protect against peroxidation. Applied to thiol-ene coupling (TEC), the allylic abstraction, degraded-chain paradigm resolved a raft of hitherto contradictory trends and findings in "click" TEC polymerization and organic synthesis methods.

Effect of 5-trans Isomer of Arachidonic Acid on Model Liposomal Membranes Studied by a Combined Simulation and Experimental Approach

Unsaturated fatty acids are found in humans predominantly in the cis configuration. Fatty acids in the trans configuration are primarily the result of human processing (trans fats), but can also be formed endogenously by radical stress. The cis-trans isomerization of fatty acids by free radicals could be connected to several pathologies. Trans fats have been linked to an increased risk of coronary artery disease; however, the reasons for the resulting pathogenesis remain unclear. Here, we investigate the effect of a mono-trans isomer of arachidonic acid (C20:4-5trans, 8cis, 11cis, 14cis) produced by free radicals in physiological concentration on a model erythrocyte membrane using a combined experimental and theoretical approach. Molecular Dynamics (MD) simulations of two model lipid bilayers containing arachidonic acid and its 5-trans isomer in 3 mol% were carried out for this purpose. The 5-trans isomer formation in the phospholipids was catalyzed by HOCH₂CH₂S· radicals, generated from the corresponding thiol by γ-irradiation, in multilamellar vesicles of SAPC. Large unilamellar vesicles were made by the extrusion method (LUVET) as a biomimetic model for cis-trans isomerization. Atomic Force Microscopy and Dynamic Light Scattering were used to measure the average size, morphology, and the z-potential of the liposomes. Both results from MD simulations and experiments are in agreement and indicate that the two model membranes display different physicochemical properties in that the bilayers containing the trans fatty acids were more ordered and more rigid than those containing solely the cis arachidonic acid. Correspondingly, the average size of the liposomes containing trans isomers was smaller than the ones without.

Alkene-assisted cis-to-trans isomerization of non-conjugated polyunsaturated alkenes

Complex [Cp*Ru(NCMe)₃][PF₆], 1a, has been identified as a cis-to-trans isomerization catalyst of various non-conjugated cis-polyalkenes under exceptional kinetic control as no alkene conjugation was observed. According to the experimental and theoretical data, the cis-trans isomerization occurred via an alkene-assisted mechanism in which one cis-double bond always served as an anchoring site. Using a combination of multinuclear NMR spectroscopic evidence and mathematical methods it was possible to determine the extent of trans isomerization.

The Reaction of Thiyl Radical with Methyl Linoleate: Completing the Picture

Cis lipids can be converted by thiols and free radicals into trans lipids, which are therefore a valuable tell-tale for free radical activity in the cell's lipidome. Our previous studies have shown that polyunsaturated lipids are isomerized by alkanethiyl radicals (S^•) in a cycle propagated by reversible double-bond addition and terminated by radical H-abstraction from the lipid. A critical flaw in this picture has long been that the reported lipid abstraction rate from radiolysis studies is faster than addition-isomerization, implying that the "cycle" must be terminating faster than it is propagating! Herein, we resolved this longstanding puzzle by combining a detailed product analysis, with reinvestigation of the time-resolved kinetics, DFT calculations of the indicated pathways, and reformulation of the radical-stasis equations. We have determined thiol-coupled products in dilute solutions arise mainly from addition to the inside position of the bisallylic group, followed by rapid intramolecular H^• transfer, yielding allylic radicals (L_ZZ + S^• ⇄ SL^• → SL'^•) that are slowly reduced by thiol (SL'^• + SH → SL'H + S^•). The first-order grow-in rate of the L_-H^• signal (k_exp^280nm) may therefore be dominated by the addition-H-translocation rather than slower direct H^•-abstraction. Steady-state kinetic analysis of the new mechanism is consistent with products and the rates and trends for polyunsaturated fatty acids (PUFAs), monounsaturated fatty acids (MUFAs), and mixtures, with and without physiological [O₂]. Implications of this new paradigm for the thiol-ene reactivity fall in an interdisciplinary research area spanning from synthetic applications to metabolomics.

Lipid Raft Formation: Key Role of Polyunsaturated Phospholipids

The forces that drive lipid raft formation are poorly understood. To date, most of the attention has focused on attractive interactions between cholesterol and high-melting lipids. Remarkably little attention has been paid to repulsive forces. Here, we show that repulsive interactions between an exchangeable mimic of cholesterol and an exchangeable mimic of a low-melting phospholipid in liquid-disordered bilayers can be much stronger than the attractive forces between this same sterol and an exchangeable mimic of a high-melting phospholipid in liquid-ordered bilayers. We conclude that polyunsaturated phospholipids have been largely overlooked as major players in lipid raft formation. This knowledge should stimulate considerable interest in controlling the levels of polyunsaturated phospholipids for the proper functioning of cell membranes.

Wine lees modulate lipid metabolism and induce fatty acid remodelling in zebrafish

This study investigates the ability of a polyphenolic extract obtained from a wine lees by-product to modulate zebrafish lipid metabolism.

Tocopherols and Tocotrienols in Common and Emerging Dietary Sources: Occurrence, Applications, and Health Benefits

Edible oils are the major natural dietary sources of tocopherols and tocotrienols, collectively known as tocols. Plant foods with low lipid content usually have negligible quantities of tocols. However, seeds and other plant food processing by-products may serve as alternative sources of edible oils with considerable contents of tocopherols and tocotrienols. Tocopherols are among the most important lipid-soluble antioxidants in food as well as in human and animal tissues. Tocopherols are found in lipid-rich regions of cells (e.g., mitochondrial membranes), fat depots, and lipoproteins such as low-density lipoprotein cholesterol. Their health benefits may also be explained by regulation of gene expression, signal transduction, and modulation of cell functions. Potential health benefits of tocols include prevention of certain types of cancer, heart disease, and other chronic ailments. Although deficiencies of tocopherol are uncommon, a continuous intake from common and novel dietary sources of tocopherols and tocotrienols is advantageous. Thus, this contribution will focus on the relevant literature on common and emerging edible oils as a source of tocols. Potential application and health effects as well as the impact of new cultivars as sources of edible oils and their processing discards are presented. Future trends and drawbacks are also briefly covered.

One- and two-electron oxidation of thiols: mechanisms, kinetics and biological fates

The oxidation of biothiols participates not only in the defense against oxidative damage but also in enzymatic catalytic mechanisms and signal transduction processes. Thiols are versatile reductants that react with oxidizing species by one- and two-electron mechanisms, leading to thiyl radicals and sulfenic acids, respectively. These intermediates, depending on the conditions, participate in further reactions that converge on different stable products. Through this review, we will describe the biologically relevant species that are able to perform these oxidations and we will analyze the mechanisms and kinetics of the one- and two-electron reactions. The processes undergone by typical low-molecular-weight thiols as well as the particularities of specific thiol proteins will be described, including the molecular determinants proposed to account for the extraordinary reactivities of peroxidatic thiols. Finally, the main fates of the thiyl radical and sulfenic acid intermediates will be summarized.

Characterization of the Aroma-Active, Phenolic, and Lipid Profiles of the Pistachio (Pistacia vera L.) Nut as Affected by the Single and Double Roasting Process

The pistachio (Pistacia vera L.) nut is one of the most widely consumed edible nuts in the world. However, it is the roasting process that makes the pistachio commercially viable and valuable as it serves as the key step to improving the nut's hallmark sensory characteristics including flavor, color, and texture. Consequently, the present study explores the effects of the single-roasting and double-roasting process on the pistachio's chemical composition, specifically aroma-active compounds, polyphenols, and lipids. Results showed the total polyphenol content of increased with the roasting treatment; however, not all phenolic compounds demonstrated this behavior. With regard to the aroma and aroma-active compounds, the results indicated that roasting process results in the development of characteristics and pleasant aroma of pistachio samples due to the Maillard reaction. With regard to lipids, the pistachio roasting treatment reduced the concentration of CN38 diacylglycerides while increasing the amount of elaidic acid.

A Promising Raman Spectroscopy Technique for the Investigation of trans and cis Cholesteryl Ester Isomers in Biological Samples

Lipid geometry is an important issue in biology and medicine. The cis-trans geometry conversion of double bonds in lipids is an endogenous process that can be mediated by sulfur-centered free radicals. Trans isomers of polyunsaturated fatty acids can be used as biological markers of free radical stress, and their presence in biological samples can be determined by synthesis and characterization of appropriate reference compounds. Fractions of plasma lipids, such as cholesteryl linoleate and arachidonate esters, are interesting targets because of their connection with membrane phospholipid turnover and their roles in cardiovascular health. In this context, Raman spectroscopy can provide a useful contribution, since Raman analysis can be performed directly on the lipid extracts without any derivatization reaction, is nondestructive, and can rapidly supply biochemical information. This study focused on the build up of Raman spectral libraries of different cis and trans isomers of cholesteryl esters to be used as references for the examination of complex biological samples and to facilitate isomer recognition. Unsaturated cholesteryl esters obtained by chemical synthesis and with different alkyl chain lengths, double bond numbers, or both, were analyzed. The potential of Raman analysis for trans isomer detection in biological samples was successfully tested on some cholesteryl ester lipid fractions from human serum. The data suggest promising applications of Raman spectroscopy in metabolomics and lipidomics.

Bleomycin-induced trans lipid formation in cell membranes and in liposome models

Bleomycin–iron complexes cause lipidcis–transisomerisation through thiyl radical formation and reactivity with unsaturated phospholipids, revealing membranes as a relevant and novel site of drug effect.

Radical-induced Cis-Trans isomerization of fatty acids: a theoretical study

Trans fatty acids (TFAs) create deleterious effects; thus their existence in humans is a great health concern. TFAs can be obtained through diet, or they can be formed endogenously by radical-induced cis to trans isomerization. The mechanism of isomerization of fatty acid catalyzed by radicals including nitrogen dioxide (NO2(•)), thiyl (RS(•)), and peroxide (ROO(•)) radicals were investigated using density functional theory. With linoleic acid, a fatty acid consisting of two homoconjugated C═C bonds, we found that the radical addition mechanism is more favorable than the hydrogen abstraction mechanism. For all investigated radicals, the isomerization catalyzed by RS(•) radical involves the smallest reaction barrier. We found that NO2(•) reactions through the N-terminus are more favorable than reactions through the O-terminus. The reaction barriers for NO2(•) catalyzed isomerizations were found to be lowered to a larger extent in polar solvent. β-carotene and lycopene were shown to protect fatty acids from isomerization by intercepting the isomerization-causing radicals.

The use of the methods of radiolysis to explore the mechanisms of free radical modifications in proteins

The method of radiolysis is based upon the interaction of ionising radiation with the solvent (water). One can form the same free radicals as in conditions of oxidative stress ((•)OH, O2(•)(-), NO2(•)…). Moreover, the quantity of reactive oxygen (ROS) or nitrogen (RNS) species formed in the irradiated medium can be calculated knowing the dose and the radiation chemical yield, G, thus this method is quantitative. The use of the method of radiolysis has provided a wealth of data, especially about the kinetics of the oxidation by various free radicals and their mechanisms, the identification of transients formed, their lifetimes and the possibility to repair them by the so-called antioxidants. In this review we have collected the most recent data about protein oxidation that might be useful to a proteomic approach. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Separation of cis-trans phospholipid isomers using reversed phase LC with high resolution MS detection

The increased presence of synthetic trans fatty acids into western diets has been shown to have deleterious effects on physiology and raising an individual's risk of developing metabolic disease, cardiovascular disease, and stroke. The importance of these fatty acids for health and the diversity of their (patho) physiological effects suggest that not only should the free trans fatty acids be studied but also monitoring the presence of these fats into the side chains of biological lipids, such as glycerophospholipids, is also essential. We developed a high resolution LC-MS method that quantitatively monitors the major lipid classes found in biospecimens in an efficient, sensitive, and robust manner while also characterizing individual lipid side chains through the use of high energy collisional dissociation (HCD) fragmentation and chromatographic alignment. We herein show how this previously described reversed phase method can baseline separate the cis-trans isomers of phosphatidylglycerol and phosphatidylcholine (PC) with two 18:1 side chains, in both positive and negative mode, as neat solutions and when spiked into a biological matrix. Endogenous PC (18:1/18:1)-cis and PC (18:1/18:1)-trans isomers were examined in mitochondrial and serum profiling studies, where rats were fed diets enriched in either trans 18:1 fatty acids or cis 18:1 fatty acids. In this study, we determined the cis:trans isomer ratios of PC (18:1/18:1) and related this ratio to dietary composition. This generalized LC-MS method enables the monitoring of trans fats in biological lipids in the context of a nontargeted method, allowing for relative quantitation and enhanced identification of unknown lipids in complex matrixes.

Lipid markers of "geometrical" radical stress: synthesis of monotrans cholesteryl ester isomers and detection in human plasma

Heteroatom-centered free radicals are able to transform cis unsaturated fatty acids to the thermodynamically more stable, but unnatural, trans configuration. The "geometrical" radical stress can be estimated in biological samples using trans fatty acid isomers as lipid markers. Regioselectivity is an important feature of the "geometrical" radical stress, because the supramolecular organization of the polyunsaturated fatty acid moieties of phospholipids can lead to preferential monotrans isomer formation. The regioisomer recognition is a crucial step, which is helped by appropriate molecular libraries available through radical-based synthetic methodologies. Cholesteryl linoleate and arachidonate esters are interesting targets for their biochemical connection with membrane phospholipid turnover and their well-known roles in cardiovascular health. The synthesis of monotrans isomers of PUFA cholesteryl esters was achieved by a thiyl radical-catalyzed cis-trans isomerization. Valuable NMR, IR, and Raman spectroscopic data have been collected for promising application in metabolomics and lipidomics. The identification of monotrans cholesteryl ester isomers was carried out in human plasma by GC, Raman, and IR analyses, demonstrating for the first time the presence of specific regiosiomers connected to free radical stress. This work helps to highlight the chemical biology approach for the access to molecular libraries applicable to biomarker development, and the cis-trans isomerization as a relevant process to be integrated in the puzzling scenario of free radical-mediated lipid modifications.

Inhibitory activity of natural occurring antioxidants on Thiyl radical-induced trans-arachidonic acid formation

trans-Fatty acids in humans not only may be obtained exogenously from food intake but also could be generated endogenously in tissues. The endogenous generation of trans-fatty acids, especially in the cell membranes induced by radical stress, is an inevitable source for the living species. Thiyl radicals generated from thiols act as the catalyst for the cis-trans isomerization of fatty acids. Arachidonic acid (5c,8c,11c,14c-20:4) with only two of the four double bonds deriving from linoleic acid in the diet can be used to differentiate the exogenous or endogenous formation of double bonds. The aim of this study is to evaluate the effective compounds in preventing thiyl radical-induced trans-arachidonic acid formation during UV irradiation in vitro. The trans-arachidonic acids were found to be 75% after 30 min UV irradiation of all-cis-arachidonic acid. Myricetin, luteolin, and quercetin had the highest thiyl radical scavenging activities, whereas sesamol, gallic acid, and vitamins A, C, and E had the lowest. The structures of flavonoids with higher thiyl radical scavenging activities were a 3',4'-o-dihydroxyl group in the B ring and a 2,3-double bond combined with a 4-keto group in the C ring. These effective compounds found in the present work may be used as lead compounds for the potential inhibitors in the formation of trans-fatty acids in vivo.

Effects of estradiol and progesterone on the reproduction of the freshwater crayfish Cherax albidus

In this study we have investigated the role of 17beta-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17beta-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17beta-estradiol was more effective than progesterone and 17beta-estradiol plus progesterone in increasing the vitellogenin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17beta-estradiol and 17beta-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid composition of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17beta-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.