In vitro production of long chain pyrrole fatty esters from carbonyl-amine reactions

An updated review of fatty acid residue-tethered heterocyclic compounds: synthetic strategies and biological significance

Heterocyclic compounds have been featured as the key building blocks for the development of biologically active molecules. In addition to being derived from renewable raw materials, fatty acids possess a variety of biological properties. The two bioactive ingredients are being combined by many researchers to produce hybrid molecules that have a number of desirable properties. Biological activities and significance of heterocyclic derivatives of fatty acids have been demonstrated in a new class of heterocyclic compounds called heterocyclic fatty acid hybrid derivatives. The significance of heterocyclic-fatty acid hybrid derivatives has been emphasized in numerous research articles over the past few years. In this review, we emphasize the development of synthetic methods and their biological evaluation for heterocyclic fatty acid derivatives. These reports, combined with the upcoming compilation, are expected to serve as comprehensive foundations and references for synthetic, preparative, and applicable methods in medicinal chemistry.

SDR9C7 catalyzes critical dehydrogenation of acylceramides for skin barrier formation

The corneocyte lipid envelope, composed of covalently bound ceramides and fatty acids, is important to the integrity of the permeability barrier in the stratum corneum, and its absence is a prime structural defect in various skin diseases associated with defective skin barrier function. SDR9C7 encodes a short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7) recently found mutated in ichthyosis. In a patient with SDR9C7 mutation and a mouse Sdr9c7-KO model, we show loss of covalent binding of epidermal ceramides to protein, a structural fault in the barrier. For reasons unresolved, protein binding requires lipoxygenase-catalyzed transformations of linoleic acid (18:2) esterified in ω-O-acylceramides. In Sdr9c7-/- epidermis, quantitative liquid chromatography-mass spectometry (LC-MS) assays revealed almost complete loss of a species of ω-O-acylceramide esterified with linoleate-9,10-trans-epoxy-11E-13-ketone; other acylceramides related to the lipoxygenase pathway were in higher abundance. Recombinant SDR9C7 catalyzed NAD+-dependent dehydrogenation of linoleate 9,10-trans-epoxy-11E-13-alcohol to the corresponding 13-ketone, while ichthyosis mutants were inactive. We propose, therefore, that the critical requirement for lipoxygenases and SDR9C7 is in producing acylceramide containing the 9,10-epoxy-11E-13-ketone, a reactive moiety known for its nonenzymatic coupling to protein. This suggests a mechanism for coupling of ceramide to protein and provides important insights into skin barrier formation and pathogenesis.

Glycolaldehyde is an endogenous source of lysine N-pyrrolation

Lysine N-pyrrolation converts lysine residues to N ^ϵ-pyrrole-l-lysine (pyrK) in a covalent modification reaction that significantly affects the chemical properties of proteins, causing them to mimic DNA. pyrK in proteins has been detected in vivo, indicating that pyrrolation occurs as an endogenous reaction. However, the source of pyrK remains unknown. In this study, on the basis of our observation in vitro that pyrK is present in oxidized low-density lipoprotein and in modified proteins with oxidized polyunsaturated fatty acids, we used LC-electrospray ionization-MS/MS coupled with a stable isotope dilution method to perform activity-guided separation of active molecules in oxidized lipids and identified glycolaldehyde (GA) as a pyrK source. The results from mechanistic experiments to study GA-mediated lysine N-pyrrolation suggested that the reactions might include GA oxidation, generating the dialdehyde glyoxal, followed by condensation reactions of lysine amino groups with GA and glyoxal. We also studied the functional significance of GA-mediated lysine N-pyrrolation in proteins and found that GA-modified proteins are recognized by apolipoprotein E, a binding target of pyrrolated proteins. Moreover, GA-modified proteins triggered an immune response to pyrrolated proteins, and monoclonal antibodies generated from mice immunized with GA-modified proteins specifically recognized pyrrolated proteins. These findings reveal that GA is an endogenous source of DNA-mimicking pyrrolated proteins and may provide mechanistic insights relevant for innate and autoimmune responses associated with glucose metabolism and oxidative stress.

A Dual Perspective of the Action of Lysine on Soybean Oil Oxidation Process Obtained by Combining 1H NMR and LC-MS: Antioxidant Effect and Generation of Lysine-Aldehyde Adducts

Little is still known about both the effect of amino acids on the oxidation course of edible oils and the modifications that the former may undergo during this process. Bearing this in mind, the objective of this work was to study the evolution of a system consisting of soybean oil with 2% of l-lysine under heating at 70 °C and stirring conditions, analyzing how the co-oxidation of the oil and of the amino acid affects their respective evolutions, and trying to obtain information about the action mechanism of lysine on soybean oil oxidation. The study of the oil progress by 1H Nuclear Magnetic Resonance (1H NMR) showed that the presence of lysine noticeably delays oil degradation and oxidation products generation in comparison with a reference oil without lysine. Regarding lysine evolution, the analysis by 1H NMR and Liquid Chromatography-Mass Spectrometry of a series of aqueous extracts obtained from the oil containing lysine over time revealed the formation of lysine adducts, most of them at the position, with n-alkanals, malondialdehyde, (E)-2-alkenals, and toxic oxygenated α β-unsaturated aldehydes. However, this latter finding does not seem enough to explain the antioxidant action of lysine.

Food Processing Antioxidants

Food processing has been carried out since ancient times as a way to preserve and improve food nutritional and organoleptic properties. Although it has some undesirable consequences, such as the losses of some nutrients and the potential formation of toxic compounds, a wide range of benefits can be enumerated. Among them, the increased total antioxidant capacity of many processed foods has been known for long. This consequence has been related to both the release or increased availability of natural antioxidants and the de novo formation of substances with antioxidant properties as a consequence of the produced reactions. This review analyzes the chemical changes produced in foods during processing with special emphasis on the formation of antioxidants as a consequence of carbonyl-amine reactions produced by both carbohydrate- and lipid-derived reactive carbonyls. It discusses the lastest advances produced in the characterization of carbonyl-amine adducts and their potential action as primary (free radical scavengers), secondary (chelating and other ways to prevent lipid oxidation), and tertiary (carbonyl scavengers as a way to avoid lipid oxidation consequences) antioxidants. Moreover, the possibility of combining amino compounds with different hydrophobicity, such as aminophospholipids and proteins, with a wide array of reactive carbonyls points out to the use of carbonyl-amine reactions as a new way to induce the formation of a great variety of substances with antioxidant properties and very variable hydrophilia/lipophilia. All presented results point out to carbonyl-amine reactions as an effective method to generate efficacious antioxidants that can be used in food technology.

Advanced glycoxidation and lipoxidation end products (AGEs and ALEs): an overview of their mechanisms of formation

Advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs) have a pathogenetic role in the development and progression of different oxidative-based diseases including diabetes, atherosclerosis, and neurological disorders. AGEs and ALEs represent a quite complex class of compounds that are formed by different mechanisms, by heterogeneous precursors and that can be formed either exogenously or endogenously. There is a wide interest in AGEs and ALEs involving different aspects of research which are essentially focused on set-up and application of analytical strategies (1) to identify, characterize, and quantify AGEs and ALEs in different pathophysiological conditions; (2) to elucidate the molecular basis of their biological effects; and (3) to discover compounds able to inhibit AGEs/ALEs damaging effects not only as biological tools aimed at validating AGEs/ALEs as drug target, but also as promising drugs. All the above-mentioned research stages require a clear picture of the chemical formation of AGEs/ALEs but this is not simple, due to the complex and heterogeneous pathways, involving different precursors and mechanisms. In view of this intricate scenario, the aim of the present review is to group the main AGEs and ALEs and to describe, for each of them, the precursors and mechanisms of formation.

Lipid peroxidation of membrane phospholipids generates hydroxy-alkenals and oxidized phospholipids active in physiological and/or pathological conditions

Polyunsaturated fatty acids (PUFAs) and their metabolites have a variety of physiological roles including: energy provision, membrane structure, cell signaling and regulation of gene expression. Lipids containing polyunsaturated fatty acids are susceptible to free radical-initiated oxidation and can participate in chain reactions that increase damage to biomolecules. Lipid peroxidation, which leads to lipid hydroperoxide formation often, occurs in response to oxidative stress. Hydroperoxides are usually reduced to their corresponding alcohols by glutathione peroxidases. However, these enzymes are decreased in certain diseases resulting in a temporary increase of lipid hydroperoxides that favors their degradation into several compounds, including hydroxy-alkenals. The best known of these are: 4-hydroxy-2-nonenal (4-HNE) and 4-hydroxy-2-hexenal (4-HHE), which derive from lipid peroxidation of n-6 and n-3 fatty acids, respectively. Compared to free radicals, these aldehydes are relatively stable and can diffuse within or even escape from the cell and attack targets far from the site of the original event. These aldehydes exhibit great reactivity with biomolecules, such as proteins, DNA, and phospholipids, generating a variety of intra and intermolecular covalent adducts. At the membrane level, proteins and amino lipids can be covalently modified by lipid peroxidation products (hydoxy-alkenals). These aldehydes can also act as bioactive molecules in physiological and/or pathological conditions. In addition this review is intended to provide an appropriate synopsis of identified effects of hydroxy-alkenals and oxidized phospholipids on cell signaling, from their intracellular production, to their action as intracellular messenger, up to their influence on transcription factors and gene expression.

Model studies on the degradation of phenylalanine initiated by lipid hydroperoxides and their secondary and tertiary oxidation products

The reaction of methyl 13-hydroperoxyoctadeca-9,11-dienoate (MeLOOH), methyl 13-hydroperoxyoctadeca-9,11,15-trienoate (MeLnOOH), methyl 13-hydroxyoctadeca-9,11-dienoate (MeLOH), methyl 13-oxooctadeca-9,11-dienoate (MeLCO), methyl 9,10-epoxy-13-hydroxy-11-octadecenoate (MeLEPOH), and methyl 9,10-epoxy-13-oxo-11-octadecenoate (MeLEPCO) with phenylalanine was studied to determine the comparative reactivity of primary, secondary, and tertiary lipid oxidation products in the Strecker degradation of amino acids. All assayed lipids were able to degrade the amino acid to a high extent, although the lipid reactivity decreased slightly in the following order: MeLEPCO > or = MeLCO > MeLEPOH > or = MeLOH > MeLOOH approximately = MeLnOOH. These data confirmed the ability of many lipid oxidation products to degrade amino acids by a Strecker-type mechanism and suggested that, once the lipid oxidation is produced, a significant Strecker degradation of surrounding amino acids should be expected. The contribution of different competitive mechanisms to this degradation is proposed, among which the conversion of the different lipid oxidation products assayed into the most reactive MeLEPCO and the fractionation of long-chain primary and secondary lipid oxidation products into short-chain aldehydes are likely to play a major role.

Contribution of lipid oxidation products to acrylamide formation in model systems

The reactions of asparagine with methyl linoleate ( 1), methyl 13-hydroperoxyoctadeca-9,11-dienoate ( 2), methyl 13-hydroxyoctadeca-9,11-dienoate ( 3), methyl 13-oxooctadeca-9,11-dienoate ( 4), methyl 9,10-epoxy-13-hydroxy-11-octadecenoate ( 5), methyl 9,10-epoxy-13-oxo-11-octadecenoate ( 6), 2,4-decadienal ( 7), 2-octenal ( 8), 4,5-epoxy-2-decenal ( 9), and benzaldehyde ( 10) were studied to determine the potential contribution of lipid derivatives to acrylamide formation in heated foodstuffs. Reaction mixtures were heated in sealed tubes for 10 min at 180 degrees C under nitrogen. The reactivity of the assayed compounds was 7 >> 9 > 4 > 2 >> 8 approximately 6 >> 10 approximately 5. The presence of compounds 1 and 3 did not result in the formation of acrylamide. These results suggested that alpha,beta,gamma,delta-diunsaturated carbonyl compounds were the most reactive compounds for this reaction followed by lipid hydroperoxides, more likely as a consequence of the thermal decomposition of these last compounds to produce alpha,beta,gamma,delta-diunsaturated carbonyl compounds. However, in the presence of glucose this reactivity changed, and compound 1/glucose mixtures showed a positive synergism (synergism factor = 1.6), which was observed neither in methyl stearate/glucose mixtures nor in the presence of antioxidants. This synergism is proposed to be a consequence of the formation of free radicals during the asparagine/glucose Maillard reaction, which oxidized the lipid and facilitated its reaction with the amino acid. These results suggest that both unoxidized and oxidized lipids are able to contribute to the conversion of asparagine into acrylamide, but unoxidized lipids need to be oxidized as a preliminary step.

Interplay between the Maillard Reaction and Lipid Peroxidation in Biochemical Systems

The Maillard reaction and lipid peroxidation are two of the most important chemical reactions that take place in biochemical systems. Both include a whole network of different reactions in which an extraordinarily complex mixture of compounds is produced in very different amounts, with both positive and negative consequences. In addition, both reactions are intimately interrelated, and the products of each reaction influence the other. Furthermore, there are common intermediates and products in both pathways; these products are usually known as advanced glycation end products (AGEs) and advanced lipoxidation end products (ALEs). Moreover, other AGE/ALEs are analogous and participate similarly in both amino acid degradation and amino phospholipid/protein polymerization by identical mechanisms. All these data suggest that the Maillard reaction and lipid peroxidation are so closely interrelated that both reactions should be considered simultaneously to understand the reaction mechanisms, kinetics, and products in the complex mixtures of carbohydrates, lipids, and proteins occurring in biochemical systems. In these systems, lipids and carbohydrates are competing in the chemical modification of amino phospholipids and proteins. Therefore, although there are significant differences between the Maillard reaction and lipid peroxidation, many aspects of both reactions can be better understood if they are included in only one general carbonyl pathway that can be initiated by both lipids and carbohydrates.

2-Alkylpyrrole formation from 4,5-epoxy-2-alkenals

N-Substituted 2-pentylpyrrole formation has been related to the etiology or the consequences of several diseases in which lipid oxidation is involved. This study describes the formation of N-substituted 2-alkylpyrroles in the reaction of 4,5-epoxy-2-alkenals with amino compounds and suggests an alternative pathway for the formation of these compounds that are nowadays commonly accepted to be produced by reaction of the lipid oxidation product 4-hydroxy-2-nonenal with primary amino compounds. The described reaction constitutes a new route for pyrrole production in the lipid peroxidation pathway when it takes place in the presence of amino compounds and implies the loss of one carbon in the 4,5-epoxy-2-alkenal during the formation of the heterocyclic ring, which is proposed to be released as formaldehyde. This reaction also confirms the high reactivity of 4,5-epoxy-2-alkenals, which are usually found in smaller amounts than other lipid oxidation products. Their importance in vivo may be underappreciated in part as a consequence of this high reactivity that brings about their rapid disappearance.

Strecker-type degradation of phenylalanine by methyl 9,10-epoxy-13-oxo-11-octadecenoate and methyl 12,13-epoxy-9-oxo-11-octadecenoate

The reaction of methyl 9,10-epoxy-13-oxo-11(E)-octadecenoate, methyl 12,13-epoxy-9-oxo-11(E)-octadecenoate, 4,5(E)-epoxy-2(E)-heptenal, and 4,5(E)-epoxy-2(E)-decenal with phenylalanine in acetonitrile-water (2:1, 1:1, and 1:2) at 80 degrees C and at different pHs and carbonyl compound/amino acid ratios was investigated both to determine if epoxyoxoene fatty esters were able to produce the Strecker-type degradation of the amino acid and to study the relative ability of oxidized long-chain fatty esters and short chain aldehydes with identical functional systems to degrade amino acids. The studied epoxyoxoene fatty esters degraded phenylalanine to phenylacetaldehyde. The mechanism of the reaction was analogous to that described for epoxyalkenals and is suggested to be produced through the corresponding imine, which is then decarboxylated and hydrolyzed. This reaction also produced a conjugated hydroxylamine, which was the origin of the long-chain pyridine-containing fatty ester isolated in the reaction and characterized as methyl 8-(6-pentylpyridin-2-yl)octanoate. Epoxyoxoene fatty esters and epoxyalkenals exhibited a similar reactivity for producing phenylacetaldehyde, therefore suggesting that nonvolatile lipid oxidation products, which are produced to a greater extent than volatile products, should be considered for determining the overall contribution of lipids to Strecker degradation of amino acids produced during nonenzymatic browning. In addition, the obtained data confirm that, analogously to carbohydrates, lipid oxidation products are also able to produce the Strecker degradation of amino acids.

Determination of pyrrolized phospholipids in oxidized phospholipid vesicles and lipoproteins

The Ehrlich reaction was optimized to determine pyrrolized phospholipids produced as a consequence of oxidative stress. The procedure consisted of the treatment of the modified phospholipids with p-(dimethylamino)benzaldehyde at a controlled acidity temperature and the spectrophotometric determination of adducts produced. The extinction coefficient of Ehrlich adducts was calculated by using 1-[1-(2-hydroxyethyl)-1H-pyrrol-2-yl]propan-1-ol (compound 1) as standard and was 56,500 M(-1)cm(-1). The response was linear and reproducible within the range of 0.051-7.65 microM of compound 1. When the assay was applied to determination of pyrrole content in ethanolamine incubated in the presence of 0.25-1mM of 4,5(E)-epoxy-2(E)-heptenal, the complete conversion of the aldehyde into the pyrrole ring was observed and the results obtained were similar to those found when compound 1 was determined by gas chromatography. When phosphatidylethanolamine was incubated in the presence of 0.5-40 mM of 4,5(E)-epoxy-2(E)-heptenal, the phospholipid was pyrrolized similarly to ethanolamine, although there was not a quantitative conversion and the amount of pyrroles produced depended on the pH of the media. Pyrrolized phospholipids were also produced when phosphatidylethanolamine multilamellar vesicles where oxidized in the presence of either Fe(3+)/ascorbic acid or ABAP (2,2'-azobis(2-methylpropionamide) dihydrochloride) and when high-density lipoproteins were incubated in the presence of Cu(2+), thereby confirming that phospholipid pyrrolization is a common consequence of oxidative stress and that Ehrlich adducts may be valid for determining this pyrrolization.

Coordinate Contribution of Lipid Oxidation and Maillard Reaction to the Nonenzymatic Food Browning

Lipid oxidation and the Maillard reaction are probably the two most important reactions in Food Science. Both include a whole network of different reactions in which an extraordinary complex mixture of compounds are obtained in very different amounts and produce important changes in food flavor, color, texture, and nutritional value, with positive and negative consequences. This article analyzes the interactions between both reactions, with special emphasis in nonenzymatic browning development, by discussing the influence of lipid oxidation products in the Maillard pathway and vice versa, as well as the existence of common intermediates and polymerization mechanisms in both reactions. The existing data suggest that both reactions are so interrelated that they should be considered simultaneously to understand the products of the Maillard reaction in the presence of lipids and vice versa, and should be included in one general pathway that can be initiated by both lipids and carbohydrates.

Effect of the pyrrole polymerization mechanism on the antioxidative activity of nonenzymatic browning reactions

The present investigation was undertaken to study how the antioxidative activity (AA) of nonenzymatic browning reactions is changing at the same time that the browning (by the pyrrole polymerization mechanism) is being produced. The antioxidative activities of eight model pyrroles (pyrrole, 1-methylpyrrole, 2,5-dimethylpyrrole, 1,2,5-trimethylpyrrole, 2-acetylpyrrole, 2-acetyl-1-methylpyrrole, pyrrole-2-carboxaldehyde, and 1-methyl-2-pyrrolecarboxaldehyde) as well as the browning reaction of 2-(1-hydroxyethyl)-1-methylpyrrole (HMP) and the dimer (DIM) produced during HMP browning were determined. The results obtained suggest that the AAs observed in nonenzymatic browning reactions are the result of the AAs of the different oxidized lipid/amino acid reaction products formed. Thus, the different pyrrole derivatives produced in these reactions had different AAs, and the highest AAs were observed for alkyl-substituted pyrroles without free alpha-positions. Because some of these pyrrole derivatives are implicated in nonenzymatic browning production and this browning production implies the loss of hydroxyl groups and the transformation of some pyrroles with one type of substitution into others, changes in AA during browning production were observed, and the resulting DIM derivative was more antioxidant than HMP or higher polymers. These results explain the AA observed in fatty acid/protein mixtures after slight oxidation and suggest that, when the pyrrole polymerization mechanism is predominant, slightly browned samples may be more antioxidant than samples in which nonenzymatic browning has been highly developed.

Comparative methyl linoleate and methyl linolenate oxidation in the presence of bovine serum albumin at several lipid/protein ratios

The oxidation of methyl linoleate (LMe) and methyl linolenate (LnMe) in the presence of bovine serum albumin (BSA) in the dark at 60 degrees C was studied to analyze the role of the type of fatty acid and the protein/lipid ratio on the relative progression of the processes involved when lipid oxidation occurs in the presence of proteins. The disappearance of the fatty acid, the formation of primary and secondary products of lipid peroxidation, the loss of amino acid residues, the production of oxidized lipid/amino acid reaction products, and the development of color and fluorescence were studied as a function of incubation time in protein/lipid samples at 10:1, 6:1, and 3:1 w/w ratios. The incubation of LMe and LnMe in the presence of BSA at 60 degrees C rapidly produced lipid peroxidation and protein damage. Although reaction rates were much faster for LnMe than for LMe, both fatty acids had similar behaviors, and LnMe seemed to be only slightly more reactive than LMe for BSA by producing a higher increase of protein pyrroles in the protein and the development of increased browning and fluorescence. The protein/lipid ratio also influenced the relative progress of the reactions implicated. Thus, a lower protein/lipid ratio increased sample oxidation and protein damage. This also produced an increased browning, in accordance with the mechanisms proposed for browning production by oxidized lipid/protein reactions. On the contrary, browning of extracted lipids increased at higher protein/lipid ratios. This opposite tendency allowed evaluation of the overall significance of the different browning processes implicated in the final colors observed, concluding that color changes observed in BSA/lipid samples were mostly a consequence of oxidized lipid/protein reactions.

Methyl linoleate oxidation in the presence of bovine serum albumin

The oxidation of methyl linoleate (LMe) in the presence of bovine serum albumin (BSA) was studied to analyze both the processes involved when lipid oxidation occurs in the presence of proteins and the relative progression of the several reactions implicated. The disappearance of LMe, the formation of primary and secondary lipid oxidation products, the loss of essential amino acids, and the production of oxidized lipid/amino acid reaction products (OLAARPs) were studied as a function of incubation time. During the first steps of lipid oxidation, LMe was converted quantitatively to methyl linoleate hydroperoxides, which were very rapidly degraded to either secondary products of lipid oxidation or OLAARPs. No significant differences were identified in the major lipid oxidation products formed in incubations with or without proteins, indicating that mechanisms for formation of these compounds are similar in both cases. In addition, no significant differences were observed between the time-courses of formation of secondary oxidation products and OLAARPs, suggesting that hydroperoxide decomposition and OLAARP formation occur simultaneously when the lipid oxidation process takes place in the presence of proteins. Furthermore, OLAARP formation seems to be an unavoidable process that should be considered as a last step in the lipid peroxidation process.

Inhibition of proteolysis in oxidized lipid-damaged proteins

The proteolysis of bovine serum albumin (BSA) modified by reaction with the lipid peroxidation product 4,5(E)-epoxy-2(E)-heptenal was studied to better understand the loss of digestibility observed in oxidized lipid-damaged proteins. BSA was incubated for different periods of time with eight concentrations of the epoxyalkenal and, then, treated for 24 h with chymotrypsin, pancreatin, Pronase, or trypsin. The treatment of BSA with the aldehyde always decreased its proteolysis in relation to that of native BSA, and this inhibition of the proteolysis was related to the concentration of the epoxyalkenal and the reaction time. In fact, this inhibition was correlated with the damage suffered by the protein as a consequence of its reaction with the aldehyde: mainly the development of browning, the denaturation of the protein, and the formation of the oxidized lipid/amino acid reaction product epsilon-N-pyrrolylnorleucine (p < or = 0.0011, 0.0045, and 0.0031, respectively). In addition, epsilon-N-pyrrolylnorleucine added at 0.1 or 1 mM inhibited the proteases assayed and suggested that the inhibition of the proteolysis observed in oxidized lipid-damaged proteins may be related to the formation and accumulation of pyrrolized amino acid residues.

Pyrrolization and Antioxidant Function of Proteins Following Oxidative Stress

The consequences of oxidative stress on microsomal proteins were analyzed by studying their pyrrolization and the antioxidative activity of the modified proteins produced. The microsomal system consisted of freshly prepared trout muscle microsomes, which were oxidized in the presence of 5 microM Cu(2+), 1 mM Fe(3+)/5 mM ascorbate, or 1 mM Cu(2+)/10 mM H(2)O(2). Pyrroles on proteins were detected by forming Ehrlich adducts with p-(dimethylamino)benzaldehyde and by determination of epsilon-N-pyrrolylnorleucine (Pnl) by capillary electrophoresis. Their antioxidative activity was studied by testing two model pyrrolized proteins (dimeric and monomeric modified bovine serum albumin: DBSA and MBSA, respectively), which were produced in the reaction of BSA and 4,5(E)-epoxy-2(E)-heptenal. These proteins were assayed at a concentration of 10-40 microg/mL, which was selected because at this concentration both DBSA and MBSA had a concentration of Pnl similar to the Pnl concentration produced in oxidized microsomes. Both DBSA and MBSA significantly (p < 0.05) protected against lipid peroxidation, assessed by the formation of thiobarbituric acid reactive substances (TBARS), and protein damage, evaluated by amino acid analysis, for the three systems assayed, and this protection was always higher than that exhibited by BSA, which was used as control. The order of effectiveness was DBSA > MBSA > BSA and was parallel to the Pnl content in the assayed proteins. These results suggest that antioxidative activity of BSA may also be related to its ability to react with lipid oxidation products and to produce modified BSA with antioxidative activity. This mechanism may also be contributing to the antioxidative activity exhibited by many proteins.

Contribution of pyrrole formation and polymerization to the nonenzymatic browning produced by amino-carbonyl reactions

Recent studies have hypothesized that pyrrole formation and polymerization may be contribute to the nonenzymatic browning produced in both oxidized lipid/protein reactions and the Maillard reaction. To develop a methodology that would allow investigation of the contribution of this browning mechanism, the kinetics of formation of color, fluorescence, and pyrrolization in 4, 5(E)-epoxy-2(E)-heptenal/lysine and linolenic acid/lysine model systems were studied. In both cases similar kinetics for the three measurements were observed at the two temperatures assayed (37 and 60 degrees C), and there was a high correlation among color, fluorescence, and pyrrolization measurements obtained as a function of incubation time. Because the color and fluorescence production in the 4,5(E)-epoxy-2(E)-heptenal/lysine system is a consequence of pyrrole formation and polymerization, the high correlations observed with the unsaturated fatty acid also suggest a contribution of the pyrrole formation and polymerization to the development of color and fluorescence observed in the fatty acid/lysine system. Although the contribution of other mechanisms cannot be discarded, all of these results suggest that when the pyrrole formation and polymerization mechanism contributes to the nonenzymatic browning of foods, a high correlation among color, fluorescence, and pyrrolization measurements should be expected.

Formation of Nepsilon-(hexanonyl)lysine in protein exposed to lipid hydroperoxide. A plausible marker for lipid hydroperoxide-derived protein modification

The objectives of this study were to estimate the structure of the lipid hydroperoxide-modified lysine residue and to prove the presence of the adducts in vivo. The reaction of lipid hydroperoxide toward the lysine moiety was investigated employing N-benzoyl-glycyl-L-lysine (Bz-Gly-Lys) as a model compound of Lys residues in protein and 13-hydroperoxyoctadecadienoic acid (13-HPODE) as a model of the lipid hydroperoxides. One of the products, compound X, was isolated from the reaction mixture of 13-HPODE and Bz-Gly-Lys and was then identified as N-benzoyl-glycyl-Nepsilon-(hexanonyl)lysine. To prove the formation of Nepsilon-(hexanonyl)lysine, named HEL, in protein exposed to the lipid hydroperoxide, the antibody to the synthetic hexanonyl protein was prepared and then characterized in detail. Using the anti-HEL antibody, the presence of HEL in the lipid hydroperoxide-modified proteins and oxidized LDL was confirmed. Furthermore, the positive staining by anti-HEL antibody was observed in human atherosclerotic lesions using an immunohistochemical technique. The amide-type adduct may be a useful marker for the lipid hydroperoxide-derived modification of biomolecules.

Modification of histidine residues by 4,5-epoxy-2-alkenals

The reactions of 4,5(E)-epoxy-2(E)-heptenal with 4-methylimidazole and N(alpha)-acetyl-L-histidine methyl ester were studied to characterize the adducts produced in the modification of histidine residues by epoxyalkenals and to develop a methodology for the determination of these adducts in protein hydrolysates. The reaction products, which were isolated and characterized, resulted in the Michael adducts produced in the addition of one of the imidazolic nitrogens to the carbon-carbon double bond of the epoxyalkenal. Only some of the theoretical isomers were produced. Thus, in the reaction with 4-methylimidazole, the main product was 4, 5-epoxy-3-(4-methylimidazol-1-yl)heptanol (88%), although the formation of 4,5-epoxy-3-(5-methylimidazol-1-yl)heptanol (12%) was also observed. On the other hand, the reaction with N(alpha)-acetyl-L-histidine methyl ester produced exclusively N(alpha)-acetyl-1-[1'-(1' ',2' '-epoxybutyl)-3'-hydroxypropyl]-L-histidine methyl ester. This last compound was used to develop a procedure for the determination of 4, 5(E)-epoxy-2(E)-heptenal-histidine adducts in protein hydrolysates. When this procedure was applied to the analysis of bovine serum albumin treated with 0.01-10 mM 4,5(E)-epoxy-2(E)-heptenal, the formation of the adduct was observed and its concentration increased with the concentration of the aldehyde and the incubation time, and was parallel to the histidine losses observed in the protein after acid hydrolysis as well as to the formation of protein carbonyls. In addition, the number of histidine residues lost in the protein was very similar to the number of adduct residues produced, suggesting that the addition reaction is the major mechanism for histidine losses suffered by proteins following their reaction with epoxyalkenals.

Feed-back inhibition of oxidative stress by oxidized lipid/amino acid reaction products

Three oxidized lipid/amino acid reaction products (OLAARPs): 1-methyl-4-pentyl-1,4-dihydropyridine-3,5-dicarbaldehyde, 1-(5-amino-1-carboxypentyl)pyrrole, and N-(carbobenzyloxy)-1(3)-[1-(formylmethyl)hexyl]-l-histidine dihydrate, were prepared and tested for antioxidative activity in a microsomal system in order to investigate the effect that OLAARP formation may be playing in the oxidative stress process. The microsomal system consisted of freshly prepared trout muscle microsomes, which were oxidized in the presence of 5 microM Cu2+, 1 mM Fe3+/5 mM ascorbate, or 1 mM Cu2+/10 mM H2O2, and the compound to be tested as antioxidant added at 50 microM. At different periods of time, samples were tested for lipid peroxidation, assessed by the formation of thiobarbituric acid reactive substances (TBARS), and protein damage, which was evaluated by the formation of protein carbonyls and amino acid analysis. The three OLAARPs and butylated hydroxytoluene significantly (p < 0.05) protected against lipid peroxidation and protein damage for the three systems assayed. On the contrary, neither the amino acids used in the preparation of OLAARPs nor alpha-tocopherol, mannitol, aminoguanidine, or 4, 5-dihydroxy-1,3-benzenedisulfonic acid exhibited this constant protection. Because OLAARPs were produced at inhibitory levels during microsomal lipid peroxidation, these results suggest that OLAARP formation may be an antioxidative defense mechanism by which oxidative stress is feed-back-inhibited, delaying the damage caused by reactive oxygen species.

Linoleic acid oxidation in the presence of amino compounds produces pyrroles by carbonyl amine reactions

The reactions of 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid (13-LOOH) and its degradation product 4,5(E)-epoxy-2(E)-decenal with butylamine and lysine were studied to determine whether pyrrole derivatives isolated in model reactions were produced in complex systems involving hydroperoxides. Incubated reaction mixtures were studied by gas chromatography coupled with mass spectrometry or high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS), and some compounds were isolated by column chromatography or semipreparative HPLC, and identified by 1H- and 13C-nuclear magnetic resonance spectroscopy and MS. The reaction of epoxyalkenals with amino groups produced two types of pyrrole derivatives: 1-substituted 2-(1'-hydroxyalkyl)pyrroles and 1-substituted pyrroles. 1-Substituted 2-(1'-hydroxyalkyl)pyrroles were responsible for the development of color and fluorescence by a polymerization reaction, which implied the formation of dipyrrylmethanes and dipyrrylmethenes. 1-Substituted pyrroles were final products in these reactions and their determination might be used as an index of oxidative stress. The above reactions were also observed between 13-LOOH and amino compounds, and suggested that the pyrrole polymerization mechanism plays a role in the fluorescence observed by reaction of hydroperoxides and amino groups.