New method for the quantitative determination of major protein carbonyls, alpha-aminoadipic and gamma-glutamic semialdehydes: investigation of the formation mechanism and chemical nature in vitro and in vivo

Exposure to Sodium p-Perfluorous Nonenoxybenzenesulfonate Induces Renal Fibrosis in Mice by Disrupting Lysine Metabolism

Environmental exposure is one driving factor of chronic kidney disease (CKD), yet the intrinsic molecular mechanisms are largely unexplored. As a persistent chemical, perfluorooctanesulfonate (PFOS) is regulated due to a great potential to induce multiple diseases, including renal fibrosis, a major pathological characteristic of CKD. It is hypothesized that sodium p-perfluorous nonenoxybenzenesulfonate (OBS), a typical alternative to PFOS, may also induce renal fibrosis. We observed distinct renal fibrosis in mice exposed to OBS. Metabolomics analysis showed that Nα-acetyllysine was the primary metabolite biomarker, whose level decreased greatly due to its excessive consumption by lysyloxidase (LOX). This suppressed the miR-140-5p expression, promoting upregulation of fibroblast growth factor 9 (FGF9), which activated the PI3K/Akt signaling pathway through fibroblast growth factor receptor 3 (FGFR3), thereby enhancing proliferation and activation of fibroblasts. Supplement of Nα-acetyllysine upregulated miR-140-5p expression, reduced expressions of FGF9 and FGFR3, and eventually ameliorated OBS-induced renal fibrosis. Similarly, treatment with miR-140-5p agomir and PI3K/Akt signaling pathway inhibitor LY294002 attenuated OBS-induced renal fibrosis. Taken together, OBS caused renal fibrosis through the LOX-Nα-acetyllysine-miR-140-5p-FGF9-FGFR3-PI3K/Akt-Bad-Bcl-2-fibroblast axis. The results of this study reveal a specific molecular axis for OBS to induce renal fibrosis and call for concerns in supervising the application of OBS.

Changes in Novel Biomarkers for Protein Oxidation in Pork Patties under Different Cooking Methods

The aim of this study was to assess the effectiveness of different biomarkers to identify the levels of protein oxidation in pork patties induced by assorted cooking methods. To achieve this purpose, pork patties prepared from longissimus dorsi were cooked using three methods (frying, steaming, and roasting) at different internal temperatures (60, 70, 80, and 90 °C). Traditional biomarkers including total carbonyl and total thiol and novel biomarkers including α-aminoadipic semialdehyde (AAS) and lysinonorleucine (LNL) were determined. Results demonstrated that total thiol and AAS were the most successful biomarkers in distinguishing the three cooking methods in relation to protein oxidation, with AAS being the most sensitive. Moreover, as indicated by the biomarkers of total thiol and AAS, frying caused the highest level of protein oxidation, while steaming resulted in the lowest level when pork patties were cooked to the internal temperatures of 70 or 80 °C.

Protein carbonylation and structural changes in porcine myofibrillar protein exposed to metal ion-H2O2-ascorbate and linoleic acid-lipoxidase oxidizing systems

The present study aimed to compare two oxidizing systems commonly present in meat for their influence on protein oxidation patterns, with emphasis on the specific lysine-derived markers for protein carbonylation (α-aminoadipic semialdehyde, AAS; lysinonorlucine, LNL) and their relationships with the common markers for protein oxidation. For this purpose, pork myofibrillar proteins (MFP, 5 mg/mL) were suspended in 0.6 M NaCl (pH 7.5) and incubated at 4 ℃ for 24 h with two oxidizing systems: (1) a metal-catalyzed oxidizing system (MOS: 10 µM FeCl3, 100 µM ascorbic acid, and 0-10 mmol/L H2O2), (2) a linoleic acid - lipoxidase oxidizing system (LOS: 7500 units of lipoxidase/mL, and 0-10 mM linoleic acid). Results showed that the amounts of AAS and LNL in both MOS- and LOS-oxidized MFP was proportional to the oxidant concentrations (H2O2 or linoleic acid), while the formation of total carbonyl and total thiol also exhibited similar oxidant-dose-dependent patterns. Meanwhile, the α-helix contents of MFP declined with oxidant concentrations irrespective of the oxidizing systems. The reducing SDS-PAGE revealed that the myosin heavy chain band started to diminish at high H2O2 concentration (5 and 10 mM) in MOS whereas at low level of linoleic acid (0.5 mM) in LOS. Overall, these results demonstrated both oxidizing systems could be involved in the formation of AAS and LNL, and that the generation of AAS and LNL can be used as reliable markers for protein oxidation, but also might be directly involved in protein structural changes and then contribute to the alternations of protein functionality.

Tandem mass tag-based proteomics analysis of protein changes in the freezing and thawing cycles of Trachurus murphyi

We investigated the proteome variations in Trachurus murphyi with different cycles of freezing and thawing (FT) under frozen storage. A total of 2,482 proteins were assessed quantitatively, of which 269 proteins were recognized as differential abundance proteins during the second FT cycle until the eighth FT cycle. Bioinformatics analysis on gene ontology (GO) functional annotation and Kyoto Encyclopedia of Genes and Genomes pathway analyses of Differential Analysis of Proteins (DAPs) indicated multiple DAPs engaged with the protein structure, metabolic enzymes, and protein turnover. In addition, some of the observed proteins were probably the underlying markers of protein oxidation (PO). The analysis of PO sites revealed the sites of PO, such as amino adipic semialdehydes, γ-glutamic semialdehydes, and Schiff bases. Bioinformatics analyses demonstrated the involvement of differentially expressed proteins in the Hippo signaling pathway (Ko04390), indicating strong protein degradation with greater numbers of FT cycles under frozen storage. It provides an insight into quality stability from a proteomics quality perspective at the molecular level. The results obtained have deepened our current understandings of the mechanisms that reveal variations in proteomes and quality, as well as help promote quality control of T. murphyi across the cold transportation chain. PRACTICAL APPLICATION: Temperature fluctuation is one of the core issues during frozen food storage and distribution faced by the frozen food industry. Fluctuation may result in microstructural changes, ice recrystallization, and protein change in frozen food products. Tandem mass tag-based methods were adopted to study proteome variations in Trachurus murphyi muscles under different cycles of freezing and thawing under frozen storage conditions in this paper. The results obtained have deepened our current understandings of the mechanisms that reveal variations in proteomes and quality, as well as help promote quality control of T. murphyi across the cold transportation chain.

Protein carbonylation in food and nutrition: a concise update

Protein oxidation is a topic of indisputable scientific interest given the impact of oxidized proteins on food quality and safety. Carbonylation is regarded as one of the most notable post-translational modifications in proteins and yet, this reaction and its consequences are poorly understood. From a mechanistic perspective, primary protein carbonyls (i.e. α-aminoadipic and γ-glutamic semialdehydes) have been linked to radical-mediated oxidative stress, but recent studies emphasize the role alternative carbonylation pathways linked to the Maillard reaction. Secondary protein carbonyls are introduced in proteins via covalent linkage of lipid carbonyls (i.e. protein-bound malondialdehyde). The high reactivity of protein carbonyls in foods and other biological systems indicates the intricate chemistry of these species and urges further research to provide insight into these molecular mechanisms and pathways. In particular, protein carbonyls are involved in the formation of aberrant and dysfunctional protein aggregates, undergo further oxidation to yield carboxylic acids of biological relevance and establish interactions with other biomolecules such as oxidizing lipids and phytochemicals. From a methodological perspective, the routine dinitrophenylhydrazine (DNPH) method is criticized not only for the lack of accuracy and consistency but also authors typically perform a poor interpretation of DNPH results, which leads to misleading conclusions. From a practical perspective, the biological relevance of protein carbonyls in the field of food science and nutrition is still a topic of debate. Though the implication of carbonylation on impaired protein functionality and poor protein digestibility is generally recognized, the underlying mechanism of such connections requires further clarification. From a medical perspective, protein carbonyls are highlighted as markers of protein oxidation, oxidative stress and disease. Yet, the specific role of specific protein carbonyls in the onset of particular biological impairments needs further investigations. Recent studies indicates that regardless of the origin (in vivo or dietary) protein carbonyls may act as signalling molecules which activate not only the endogenous antioxidant defences but also implicate the immune system. The present paper concisely reviews the most recent advances in this topic to identify, when applicable, potential fields of interest for future studies.

Oxidative deamination of lysine residues by polyphenols generates an equilibrium of aldehyde and 2-piperidinol products

Polyphenols, especially catechol-type polyphenols, exhibit lysyl oxidase-like activity and mediate oxidative deamination of lysine residues in proteins. Previous studies have shown that polyphenol-mediated oxidative deamination of lysine residues can be associated with altered electrical properties of proteins and increased crossreactivity with natural immunoglobulin M antibodies. This interaction suggested that oxidized proteins could act as innate antigens and elicit an innate immune response. However, the structural basis for oxidatively deaminated lysine residues remains unclear. In the present study, to establish the chemistry of lysine oxidation, we characterized oxidation products obtained via incubation of the lysine analog N-biotinyl-5-aminopentylamine with eggshell membranes containing lysyl oxidase and identified a unique six-membered ring 2-piperidinol derivative equilibrated with a ring-open product (aldehyde) as the major product. By monitoring these aldehyde-2-piperidinol products, we evaluated the lysyl oxidase-like activity of polyphenols. We also observed that this reaction was mediated by some polyphenols, especially o-diphenolic-type polyphenols, in the presence of copper ions. Interestingly, the natural immunoglobulin M monoclonal antibody recognized these aldehyde-2-piperidinol products as an innate epitope. These findings establish the existence of a dynamic equilibrium of oxidized lysine and provide important insights into the chemopreventive function of dietary polyphenols for chronic diseases.

Sodium sulfite causes gastric mucosal cell death by inducing oxidative stress

Sulfites are commonly used as a preservative and antioxidant additives in the food industry. Sulfites are absorbed by the gastrointestinal tract and distributed essentially to all body tissues. Although sulfites have been believed to be safe food additives, some studies have shown that they exhibit adverse effects in various tissues. In this study, we examined the cytotoxic effect of sodium sulfite (Na₂SO₃) against rat gastric mucosal cells (RGM1) and further investigated its underlying molecular mechanism. We demonstrated that exposure to Na₂SO₃ exerts significant cytotoxicity in RGM1 cells through induction of oxidative stress. Exposure of RGM1 cells to Na₂SO₃ caused a significant formation of protein carbonyls and 8-hydroxy-2'-deoxyguanosine, major oxidative stress markers, with a concomitant accumulation of carbonylated protein-related aggregates. Furthermore, we found that incubation of lysozyme with Na₂SO₃ evokes protein carbonylation and aggregation via the metal ion-catalyzed free radical formation derived from Na₂SO₃. Our results suggest that Na₂SO₃ might lead to gastric tissue injury via induction of oxidative stress by the formation of Na₂SO₃-related free radicals.

Protein oxidation - Formation mechanisms, detection and relevance as biomarkers in human diseases

Generation of reactive oxygen species and related oxidants is an inevitable consequence of life. Proteins are major targets for oxidation reactions, because of their rapid reaction rates with oxidants and their high abundance in cells, extracellular tissues, and body fluids. Additionally, oxidative stress is able to degrade lipids and carbohydrates to highly reactive intermediates, which eventually attack proteins at various functional sites. Consequently, a wide variety of distinct posttranslational protein modifications is formed by protein oxidation, glycoxidation, and lipoxidation. Reversible modifications are relevant in physiological processes and constitute signaling mechanisms ("redox signaling"), while non-reversible modifications may contribute to pathological situations and several diseases. A rising number of publications provide evidence for their involvement in the onset and progression of diseases as well as aging processes. Certain protein oxidation products are chemically stable and formed in large quantity, which makes them promising candidates to become biomarkers of oxidative damage. Moreover, progress in the development of detection and quantification methods facilitates analysis time and effort and contributes to their future applicability in clinical routine. The present review outlines the most important classes and selected examples of oxidative protein modifications, elucidates the chemistry beyond their formation and discusses available methods for detection and analysis. Furthermore, the relevance and potential of protein modifications as biomarkers in the context of disease and aging is summarized.

Allysine and α-Aminoadipic Acid as Markers of the Glyco-Oxidative Damage to Human Serum Albumin under Pathological Glucose Concentrations

Understanding the molecular basis of the disease is of the utmost scientific interest as it contributes to the development of targeted strategies of prevention, diagnosis, and therapy. Protein carbonylation is a typical feature of glyco-oxidative stress and takes place in health disorders such as diabetes. Allysine as well as its oxidation product, the α-amino adipic acid (α-AA) have been found to be markers of diabetes risk whereas little is known about the chemistry involved in its formation under hyperglycemic conditions. To provide insight into this issue, human serum albumin was incubated in the presence of FeCl3 (25 μM) and increasing glucose concentrations for 32 h at 37 °C. These concentrations were selected to simulate (i) physiological fasting plasma concentration (4 mM), (ii) pathological pre-diabetes fasting plasma concentration (8 mM), and pathological diabetes fasting plasma concentration (12 mM) of glucose. While both allysine and α-AA were found to increase with increasing glucose concentrations, the carboxylic acid was only detected at pathological glucose concentrations and appeared to be a more reliable indicator of glyco-oxidative stress. The underlying chemical mechanisms of lysine glycation as well as of the depletion of tryptophan and formation of fluorescent and colored advanced glycation products are discussed.

Analysis of Protein Oxidation in Food and Feed Products

Food and feed proteins are subject to oxidation reactions during production, processing, and storage. Several individual oxidized amino acids have been described in model systems and food; however, protein oxidation in food is still mostly assessed by the analysis of protein carbonylation. In the present review, the chemistry of protein oxidation and its implications for protein functionality, food flavor, and nutritional physiology are briefly summarized. Limitations of generic methods targeting redox-relevant functional groups and properties of typical reaction products, such as the determination of protein carbonyls and fluorescence spectroscopy, are presented. Methods for the quantitation of individual oxidation products of susceptible amino acids, such as cysteine, methionine, phenylalanine, tyrosine, and tryptophan, are reported. Special regard is paid to limitations resulting from the required hydrolysis procedures and unintended formation of the analytes during sample pretreatment. If available, results from food analysis obtained by different methods are compared. Suggestions and requirements for future works on protein oxidation in food and nutrition are given.

Investigation of the effect of sodium nitrite on protein oxidation markers in food protein suspensions

The aim of this study is to investigate the effect of sodium nitrite (NaNO₂ ) on protein oxidation and the use of 3-nitrotyrosine (3NT) as a protein oxidation marker in suspensions of the food protein. Food proteins, namely bovine serum albumin, casein, and myofibrillar protein, were suspended in 100 mM sodium phosphate buffer and nitrated with 25 µM iron (III) chloride, 2.5 mM hydrogen peroxide, and 150 mg/kg NaNO₂ at 37°C for a period of 24 hr. The food protein suspensions were analyzed at different sampling periods for the loss of tryptophan (TRY) residues as well as the formation of Schiff bases (SBs), protein carbonyls, 3NT, and dityrosine (DT). It was found that NaNO₂ has pro-oxidant activity in NaNO₂ -added food protein suspensions due to the increased amounts of SBs, protein carbonyls, 3NT, and DT as well as decreased TRY fluorescence. Positive correlations between the 3NT and other protein oxidation markers except for TRY fluorescence were found in NaNO₂ -added food protein suspensions. In conclusion, these findings on the detection of 3NT indicate that it might be a useful tool as a new protein oxidation biomarker in food samples. PRACTICAL APPLICATIONS: Sodium nitrite (NaNO₂ ) supports protein oxidation in different food protein suspension. 3-nitrotyrosine (3NT) was found in food protein suspensions and can be a potential biomarker for protein nitration in food sample due to potential relationship between 3NT and other oxidation markers. The results showed that this study has formed novel insight into interaction between NaNO₂ and food proteins and indicate that it might affect the food quality and its nutritional value. Moreover, the relationship between protein oxidation/nitration and food quality as well as the comprehension of the scientific and technological meaning of these phenomena has been hindered because of the lack of knowledge about the basic chemistry behind the protein oxidation and nitration pathways. For the clarification of these phenomena, further studies are still needed.

Urinary Metabolomic Markers of Protein Glycation, Oxidation, and Nitration in Early-Stage Decline in Metabolic, Vascular, and Renal Health

Glycation, oxidation, nitration, and crosslinking of proteins are implicated in the pathogenic mechanisms of type 2 diabetes, cardiovascular disease, and chronic kidney disease. Related modified amino acids formed by proteolysis are excreted in urine. We quantified urinary levels of these metabolites and branched-chain amino acids (BCAAs) in healthy subjects and assessed changes in early-stage decline in metabolic, vascular, and renal health and explored their diagnostic utility for a noninvasive health screen. We recruited 200 human subjects with early-stage health decline and healthy controls. Urinary amino acid metabolites were determined by stable isotopic dilution analysis liquid chromatography-tandem mass spectrometry. Machine learning was applied to optimise and validate algorithms to discriminate between study groups for potential diagnostic utility. Urinary analyte changes were as follows: impaired metabolic health-increased N ε -carboxymethyl-lysine, glucosepane, glutamic semialdehyde, and pyrraline; impaired vascular health-increased glucosepane; and impaired renal health-increased BCAAs and decreased N ε -(γ-glutamyl)lysine. Algorithms combining subject age, BMI, and BCAAs discriminated between healthy controls and impaired metabolic, vascular, and renal health study groups with accuracy of 84%, 72%, and 90%, respectively. In 2-step analysis, algorithms combining subject age, BMI, and urinary N ε -fructosyl-lysine and valine discriminated between healthy controls and impaired health (any type), accuracy of 78%, and then between types of health impairment with accuracy of 69%-78% (cf. random selection 33%). From likelihood ratios, this provided small, moderate, and conclusive evidence of early-stage cardiovascular, metabolic, and renal disease with diagnostic odds ratios of 6 - 7, 26 - 28, and 34 - 79, respectively. We conclude that measurement of urinary glycated, oxidized, crosslinked, and branched-chain amino acids provides the basis for a noninvasive health screen for early-stage health decline in metabolic, vascular, and renal health.

Malondialdehyde interferes with the formation and detection of primary carbonyls in oxidized proteins

Carbonylation is one of the most remarkable expressions of the oxidative damage to proteins and the DNPH method the most common procedure to assess protein oxidation in biological samples. The present study was elicited by two hypotheses: i) is malondialdehyde, as a reactive dicarbonyl, able to induce the formation of allysine through a Maillard-type reaction? and ii) to which extent does the attachment of MDA to proteins interfere in the assessment of protein carbonyls using the DNPH method? Human serum albumin (HSA), human hemoglobin (HEM) and β-lactoglobulin (LAC) (5 mg/mL) were incubated with MDA (0.25 mM) for 24 h at 37 °C (HSA and HEM) or 80 °C (LAC). Results showed that MDA was unable to induce oxidative deamination of lysine residues and instead, formed stable and fluorescent adducts with proteins. Such adducts were tagged by the DNPH method, accounting for most of the protein hydrazones quantified. This interfering effect was observed in a wide range of MDA concentrations (0.05-1 mM). Being aware of its limitations, protein scientists should accurately interpret results from the DNPH method, and apply, when required, other methodologies such as chromatographic methods to detect specific primary oxidation products such as allysine.

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.

Protein oxidation and in vitro digestibility of heat-treated fermented sausages: How do they change with the effect of lipid formulation during processing?

In the present work, it was aimed to evaluate the oxidative stress indicators and in vitro digestibility during the processing of heat-treated Turkish sausages (sucuk) manufactured using different lipid formulations. The utilization of olive oil in sausage formulations had considerable impacts on proximate composition, pH, and water activity. The increased olive oil content increased primary lipid oxidation products, whereas it decreased the secondary ones. The use of olive oil increased the total carbonyl content, while it decreased the α-aminoadipic semialdehyde concentration. In general, pepsin, trypsin, and α-chymotrypsin activities of the treatments were similar to each other. The heat treatment during the processing significantly increased most of the oxidation markers. Though strong correlations were recorded between specific oxidation markers, no relationship was detected between oxidation parameters and in vitro digestibility. The results indicated that the lipid formulation and processing operations had significant impact on chemical and functional properties of heat-treated fermented sausages, within the complex interrelationships between oxidation mechanisms. PRACTICAL APPLICATIONS: The present work pointed out the changes and correlations between specific oxidation markers and in vitro digestibility of heat-treated fermented sausages during the production procedure. Oxidation reactions that occur in both proteins and lipids could have drastic impact on overall quality; for this reason, it is of great importance to provide the data for lightening these impacts regarding the product types and production applications. Since heat-treated muscle foods are widely manufactured to meet industrial needs, the data obtained from this research would contribute to understand the effects of formulation and processing operations in the formation of oxidation products and change in digestibility, thereby to pioneer further research on this topic.

Antioxidant and pro-oxidant actions of resveratrol on human serum albumin in the presence of toxic diabetes metabolites: Glyoxal and methyl-glyoxal

Methylglyoxal (MGO) and glyoxal (GO) are attracting considerable attention because of their role in the onset of diabetes symptoms. Therefore, to comprehend the molecular fundamentals of their pathological actions is of the utmost importance. In this study, the molecular interactions between resveratrol (RES) and human serum albumin (HSA) and the ability of the stilbene to counteract the oxidative damage caused by pathological concentrations of MGO and GO to the human plasma protein, was assessed. The oxidation of Cys34 in HSA as well as the formation of specific protein semialdehydes AAS (α-aminoadipic), GGS (γ-glutamic) and the accumulation of Advanced Glycation End-products (AGEs) was investigated. Resveratrol was found to neutralize both α-dicarbonyls by forming adducts detected by HESI-Orbitrap-MS. This antioxidant action was manifested in a significant reduction of AGEs. However, RES-α-dicarbonyl conjugates oxidized Cys34 and lysine, arginine and/or proline by a nucleophilic attack on SH and ε-NH groups in HSA. The formation of specific semialdehydes in HSA after incubation with GO and MGO at pathological concentrations was reported for the first time in this study, and may be used as early and specific biomarkers of the oxidative stress undergone by diabetic patients. The pro-oxidative role of the RES-α-dicarbonyl conjugates should be further investigated to clarify whether this action leads to positive or harmful clinical consequences. The biological relevance of human protein carbonylation as a redox signaling mechanism and/or as a reflection of oxidative damage and disease should also be studied in future works.

Protein Oxidation and Sensory Quality of Brine-Injected Pork Loins Added Ascorbate or Extracts of Green Tea or Maté during Chill-Storage in High-Oxygen Modified Atmosphere

Background: Ascorbate is often applied to enhance stability and robustness of brine-injected pork chops sold for retail, but may affect protein oxidation, while plant extracts are potential substitutes. Methods: Brine-injected pork chops (weight-gain ~12%, NaCl ~0.9%) prepared with ascorbate (225 ppm), green tea extract (25 ppm gallic acid equivalents (GAE)), or maté extract (25 ppm GAE) stored (5 °C, seven days) in high-oxygen atmosphere packaging (MAP: 80% O₂ and 20% CO₂) were analyzed for color changes, sensory quality, and protein oxidation compared to a control without antioxidant. Results: No significant differences were observed for green tea and maté extracts as compared to ascorbate when evaluated based on lipid oxidation derived off-flavors, except for stale flavor, which maté significantly reduced. All treatments increased the level of the protein oxidation product, α-aminoadipic semialdehyde as compared to the control, and ascorbate was further found to increase thiol loss and protein cross-linking, with a concomitant decrease in the sensory perceived tenderness. Conclusions: Green tea and maté were found to equally protect against lipid oxidation derived off-flavors, and maté showed less prooxidative activity towards proteins as compared to ascorbate, resulting in more tender meat. Maté is a valuable substitute for ascorbate in brine-injected pork chops.

Unrestricted Mass Spectrometric Data Analysis for Identification, Localization, and Quantification of Oxidative Protein Modifications

Oxidation generates multiple diverse post-translational modifications resulting in changes in protein structure and function associated with a wide range of diseases. Of these modifications, carbonylations have often been used as hallmarks of oxidative damage. However, accumulating evidence supports the hypothesis that other oxidation products may be quantitatively more important under physiological conditions. To address this issue, we have developed a holistic mass spectrometry-based approach for the simultaneous identification, localization, and quantification of a broad range of oxidative modifications based on so-called "dependent peptides". The strategy involves unrestricted database searches with rigorous filtering focusing on oxidative modifications. The approach was applied to bovine serum albumin and human serum proteins subjected to metal ion-catalyzed oxidation, resulting in the identification of a wide range of different oxidative modifications. The most common modification in the oxidized samples is hydroxylation, but carbonylation, decarboxylation, and dihydroxylation are also abundant, while carbonylation showed the largest increase in abundance relative to nonoxidized samples. Site-specific localization of modified residues reveals several "oxidation hotspots" showing high levels of modification occupancy, including specific histidine, tryptophan, methionine, glutamate, and aspartate residues. The majority of the modifications, however, occur at low occupancy levels on a diversity of side chains.

High sensitivity HPLC method for determination of the allysine concentration in tissue by use of a naphthol derivative

Common to all fibrotic and metastatic diseases is the uncontrollable remodeling of tissue that leads to the accumulation of fibrous connective tissue components such as collagen and elastin. Build-up of fibrous tissue occurs through the cross-linking of collagen or elastin monomers, which is initiated through the oxidation of lysine residues to form α-aminoadipic-δ-semialdehyde (allysine). To provide a measure of the extent of collagen oxidation in disease models of fibrosis or metastasis, a rapid, sensitive HPLC method was developed to quantify the amount of allysine present in tissue. Allysine was reacted with sodium 2-naphthol-7-sulfonate under conditions typically applied for acid hydrolysis of tissues (6M HCl, 110°C, 24h) to prepare AL-NP, a fluorescent bis-naphthol derivative of allysine. High performance liquid chromatography was applied for analysis of allysine content. Under optimal reaction and detection conditions, successful separation of AL-NP was achieved with excellent analytical performance attained. Good linear relationship (R²=0.994) between peak area and concentration for AL-NP was attained for 0.35-175pmol of analyte. A detection limit of 0.02pmol in the standard sample with a 20μL injection was achieved for AL-NP, with satisfactory recovery from 88 to 100% determined. The method was applied in the quantification of allysine in healthy and fibrotic mouse lung tissue, with the fibrotic tissue showing a 2.5 fold increase in the content of allysine.

Identification of Polyphenol-Specific Innate Epitopes That Originated from a Resveratrol Analogue

Polyphenols have received a significant amount of attention in disease prevention because of their unique chemical and biological properties. However, the underlying molecular mechanism for their beneficial effects remains unclear. We have now identified a polyphenol as a source of innate epitopes detected in natural IgM and established a unique gain-of-function mechanism in the formation of innate epitopes by polyphenol via the polymerization of proteins. Upon incubation with bovine serum albumin (BSA) under physiological conditions, several polyphenols converted the protein into the innate epitopes recognized by the IgM Abs. Interestingly, piceatannol, a naturally occurring hydroxylated analogue of a red wine polyphenol, resveratrol, mediated the modification of BSA, whose polymerized form was specifically recognized by the IgMs. The piceatannol-mediated polymerization of the protein was associated with the formation of a lysine-derived cross-link, dehydrolysinonorleucine. In addition, an oxidatively deaminated product, α-aminoadipic semialdehyde, was detected as a potential precursor for the cross-link in the piceatannol-treated BSA, suggesting that the polymerization of the protein might be mediated by the oxidation of a lysine residue by piceatannol followed by a Schiff base reaction with the ε-amino group of an unoxidized lysine residue. The results of this study established a novel mechanism for the formation of innate epitopes by small dietary molecules and support the notion that many of the beneficial effects of polyphenols could be attributed, at least in part, to their lysyl oxidase-like activity. They also suggest that resveratrol may have beneficial effects on human health because of its conversion to piceatannol.

Effect of sodium ascorbate and sodium nitrite on protein and lipid oxidation in dry fermented sausages

The effects of sodium nitrite and ascorbate on lipid and protein oxidation were studied during the ripening process of dry fermented sausages. Samples were taken at day 0, 2, 8, 14, 21 and 28 of ripening to assess lipid (malondialdehyde) and protein (carbonyls and sulfhydryl groups) oxidation. Sodium ascorbate and nitrite were separately able to reduce the formation of malondialdehyde. Their combined addition resulted in higher amounts of carbonyl compounds compared to their separate addition or the treatment without any of both compounds. Moreover, sodium nitrite limited the formation of γ-glutamic semialdehyde whereas sodium ascorbate showed a pro-oxidant effect. A loss of thiol groups was observed during ripening, which was not affected by the use of sodium ascorbate nor sodium nitrite. In conclusion, sodium nitrite and ascorbate affected protein and lipid oxidation in different manners. The possible pro-oxidant effect of their combined addition on carbonyl formation might influence the technological and sensory properties of these products.

Apple phenolics as inhibitors of the carbonylation pathway during in vitro metal-catalyzed oxidation of myofibrillar proteins

The effect of apple phenolics on the oxidative damage caused to myofibrillar proteins by an in vitro metal-catalyzed oxidation system was investigated. Three pure phenolic compounds (chlorogenic acid, (-)-epicatechin and phloridzin) and an apple peel extract were added to myofibrillar proteins in three concentrations (50, 100 and 200μM), and a blank treatment was included as a control. All suspensions were subjected to Fe(3+)/H2O2 oxidation at 37°C during 10days, and protein oxidation was evaluated as carbonylation (α-amino adipic and γ-glutamic semialdehydes) and Schiff base cross-links. Significant inhibition by apple phenolics was found as compared to the control treatment, with (-)-epicatechin being the most efficient antioxidant and phloridzin showing the weakest antioxidant effect. The higher concentrations of apple extract showed effective antioxidant activity against protein oxidation in myofibrillar proteins, emphasizing the potential of apple by-products as natural inhibitors of protein oxidation in meat products.

Oxidative Deamination of Serum Albumins by (-)-Epigallocatechin-3-O-Gallate: A Potential Mechanism for the Formation of Innate Antigens by Antioxidants

(-)-Epigallocatechin-3-O-gallate (EGCG), the most abundant polyphenol in green tea, mediates the oxidative modification of proteins, generating protein carbonyls. However, the underlying molecular mechanism remains unclear. Here we analyzed the EGCG-derived intermediates generated upon incubation with the human serum albumin (HSA) and established that EGCG selectively oxidized the lysine residues via its oxidative deamination activity. In addition, we characterized the EGCG-oxidized proteins and discovered that the EGCG could be an endogenous source of the electrically-transformed proteins that could be recognized by the natural antibodies. When HSA was incubated with EGCG in the phosphate-buffered saline (pH 7.4) at 37°C, the protein carbonylation was associated with the formation of EGCG-derived products, such as the protein-bound EGCG, oxidized EGCG, and aminated EGCG. The aminated EGCG was also detected in the sera from the mice treated with EGCG in vivo. EGCG selectively oxidized lysine residues at the EGCG-binding domains in HSA to generate an oxidatively deaminated product, aminoadipic semialdehyde. In addition, EGCG treatment results in the increased negative charge of the protein due to the oxidative deamination of the lysine residues. More strikingly, the formation of protein carbonyls by EGCG markedly increased its cross-reactivity with the natural IgM antibodies. These findings suggest that many of the beneficial effects of EGCG may be partly attributed to its oxidative deamination activity, generating the oxidized proteins as a target of natural antibodies.

Influence of the Oxidation States of 4-Methylcatechol and Catechin on the Oxidative Stability of β-Lactoglobulin

Chemical interactions between proteins and phenols affect the overall oxidative stability of a given biological system. To investigate the effect of protein-phenol adduct formation on the oxidative stability of β-lactoglobulin (β-LG), the protein was left to react with an equimolar concentration of 4-methylcatechol (4MC), catechin (Cat), or their respective quinone forms, 4-methylbenzoquinone (4MBQ) and catechin-quinone (CatQ), and subsequently subjected to metal-catalyzed oxidation by Fe(II)/H2O2 for 20 days at 37 °C. The reaction with 4MBQ resulted in 60% thiol loss and 22% loss of amino groups, whereas the addition of 4MC resulted in 12% thiol loss. The reaction with Cat or CatQ resulted in no apparent modification of β-LG. The oxidative stability of β-LG after reaction with each of 4MC, 4MBQ, Cat, or CatQ was impaired. Especially 4MC and 4MBQ were found to be pro-oxidative toward α-aminoadipic semialdehyde and γ-glutamic semialdehyde formation as well as the generation of fluorescent Schiff base products. The changes observed were ascribed to the redirection of oxidation as a result of the blocking of thiol groups but also to the oxidative deamination pathway, accelerating the production of semialdehydes and subsequently Schiff base structures.

Analysis of protein carbonylation--pitfalls and promise in commonly used methods

Oxidation of proteins has received a lot of attention in the last decades due to the fact that they have been shown to accumulate and to be implicated in the progression and the pathophysiology of several diseases such as Alzheimer, coronary heart diseases, etc. This has also resulted in the fact that research scientists are becoming more eager to be able to measure accurately the level of oxidized protein in biological materials, and to determine the precise site of the oxidative attack on the protein, in order to get insights into the molecular mechanisms involved in the progression of diseases. Several methods for measuring protein carbonylation have been implemented in different laboratories around the world. However, to date no methods prevail as the most accurate, reliable, and robust. The present paper aims at giving an overview of the common methods used to determine protein carbonylation in biological material as well as to highlight the limitations and the potential. The ultimate goal is to give quick tips for a rapid decision making when a method has to be selected and taking into consideration the advantage and drawback of the methods.

Carbonylation of myofibrillar proteins through the maillard pathway: effect of reducing sugars and reaction temperature

Carbonylation is recognized as one of the most remarkable chemical modifications in oxidized proteins and is generally ascribed to the direct attack of free radicals to basic amino acid residues. The purpose of this work was to investigate the formation of specific carbonyls, α-aminoadipic and γ-glutamic semialdehydes (AAS and GGS, respectively), in myofibrillar proteins (MP) through a Maillard-type pathway in the presence of reducing sugars. The present study confirmed the concurrent formation of protein carbonyls and advanced glycation end-products (AGEs) during incubation (80 °C/48 h) of MP (4 mg/mL) in the presence of reducing sugars (0.5 M). Copper irons (10 μM) were found to promote the formation of protein carbonyls, and a specific inhibitor of the Maillard reaction (0.02 M pyridoxamine) blocked the carbonylation process which emphasize the occurrence of a Maillard-type pathway. The Maillard-mediated carbonylation occurred in a range of reducing sugars (0.02-0.5 M) and reaction temperatures (4-110 °C) compatible with food systems. Upcoming studies on this topic may contribute further to shed light on the complex interactions between protein oxidation and the Maillard reaction and the impact of the protein damage on food quality and human health.

Dietary supplementation of krill oil attenuates inflammation and oxidative stress in experimental ulcerative colitis in rats

OBJECTIVE

To evaluate the effects of krill oil (KO) on inflammation and redox status in dextran sulfate sodium (DSS)-induced colitis in rats.

MATERIALS AND METHODS

Thirty male Wistar rats were divided into three groups: Control, DSS, and DSS + KO 5% in a 4-week diet study. Colitis was induced by 5% DSS in the drinking water the last week of the experiment. Weight and disease activity index (DAI), colon length, histological combined score (HCS), colon levels of selected cytokines and prostaglandins, markers of protein oxidative damage, fatty acid profile, and expression of selected genes were measured.

RESULTS

Rats in the DSS group increased their DAI and HCS compared with healthy controls. The colon length was significantly preserved after KO diet. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β were elevated in the DSS group compared with controls. Cytokines and HCS were nonsignificantly lower in the KO versus the DSS group. Prostaglandin (PG)E(3) increased significantly in the KO versus the other groups. Peroxisome proliferator-activated receptor (PPAR)-γ expression was nonsignificantly increased while PPAR-γ coactivator 1α (Pparg1α) expression increased significantly after KO. The levels of protein oxidation markers decreased significantly.

CONCLUSIONS

KO showed protective potential against DSS colitis based on the preservation of colon length, reduction of oxidative markers and the consistent beneficial changes of HCS, cytokine, and (PG)E(3) levels, as well as PPAR-γ and Pparg1α expression compared with DSS alone. These findings indicate an anti-inflammatory and a protein antioxidant effect of KO.

Optimization and application of microwave-assisted acid hydrolysis for rapid quantification of protein oxidation markers using LC-MS

Simple and efficient microwave-assisted acid hydrolysis (MAAH) of proteins was used for rapid quantification of α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) as major protein oxidation markers. The precursor amino acid residues corresponding to AAS and GGS in oxidized proteins were derivatized by reductive amination with sodium cyanoborohydride (NaCNBH(3)) and p-aminobenzoic acid (ABA) followed by MAAH to generate the marker derivatives AAS-ABA and GGS-ABA. The quantification was performed using electrospray ionization liquid chromatography-mass spectrometry (ESI LC-MS). The important parameters for hydrolysis were optimized, which include the temperature, the reaction time, the acid concentration and volume as well as the microwave power. Compared to the conventional acid hydrolysis of 18-24h using 6-12 M HCl at 110°C applied commonly in the literature and also in this work, MAAH of proteins can be completed as fast as in only 2-10 min and, additionally, with a 3-5 times higher yield of the final derivatization products. Furthermore, a better agreement between the ratio of the detected derivatization products and the theoretical yields from the studied protein has also been achieved, which indicates that MAAH may serve as a more reliable method of acid hydrolysis for this purpose than that with conventional thermal heating. The MAAH method is demonstrated to be a time-saving, reproducible and efficient technique for studying AAS and GGS as protein oxidation markers using LC-MS.

Fluorescent HPLC for the detection of specific protein oxidation carbonyls - α-aminoadipic and γ-glutamic semialdehydes - in meat systems

Precise methodologies for the routine analysis of particular protein carbonyls are required in order to progress in this topic of increasing interest. The present paper originally describes the application of an improved method for the detection of α-aminoadipic and γ-glutamic semialdehydes in a meat system by using a derivatization procedure with p-amino-benzoic acid (ABA) followed by fluorescent high-performance liquid chromatography (HPLC). The method development comprises i) the description of a simple HPLC program which allows the efficient separation of the ABA and the key standard compounds and ii) the optimization of the procedure for the preparation of a meat sample in order to maximize the fluorescent signal for both protein carbonyls. Furthermore, the suitability of this method is evaluated by applying the technique to porcine burger patties. The present procedure enables an accurate and relatively fast analysis of both semialdehydes in meat samples in which they could play an interesting role as reliable indicators of protein oxidation.

Protein carbonylation and water-holding capacity of pork subjected to frozen storage: effect of muscle type, premincing, and packaging

The present work aimed to study the relationship between protein carbonylation and the loss of water-holding capacity (WHC) occurring during frozen storage of porcine muscles. Pork samples corresponding to two different muscle types, glycolytic M. longissimus dorsi (LD) and oxidative M. psoas major (PM), and subjected to two different premincing, minced (MINCED) and intact pork pieces (INTACT), and packaging, vacuum packaged (VACUUM) and packed in oxygen-permeable bags (OXYGEN), procedures were frozen (-18 °C/12 weeks) and analyzed at sampling times upon thawing (weeks 1, 4, 8, and 12) for the relative amount of specific protein carbonyls, α-aminoadipic and γ-glutamic semialdehydes (AAS and GGS, respectively), and their ability to hold water using two different techniques. The formation of protein carbonyls occurred concomitantly with the loss of WHC, and both phenomena were found to be more intense in LD muscles and in MINCED and OXYGEN pork samples. The loss in WHC was from ca. 10 to 30% in 12 weeks, depending on the method of determination. Plausible mechanisms by which protein carbonylation may decrease the WHC of pork samples are thoroughly discussed in the present paper. Besides the likely impact of protein carbonylation in the water-myofibrillar protein relationships, the implication of AAS and GGS in further reactions including plausible cross-linking would explain the decrease of these semialdehydes by the end of frozen storage and would reinforce their liability in the loss of WHC of porcine muscles. The exact nature of these reactions, however, should be investigated in further studies.

A targeted mass spectrometry-based approach for the identification and characterization of proteins containing α-aminoadipic and γ-glutamic semialdehyde residues

The site-specific identification of α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) residues in proteins is reported. Semialdehydic protein modifications result from the metal-catalyzed oxidation of Lys or Arg and Pro residues, respectively. Most of the analytical methods for the analysis of protein carbonylation measure change to the global level of carbonylation and fail to provide details regarding protein identity, site, and chemical nature of the carbonylation. In this work, we used a targeted approach, which combines chemical labeling, enrichment, and tandem mass spectrometric analysis, for the site-specific identification of AAS and GGS sites in proteins. The approach is applied to in vitro oxidized glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and an untreated biological sample, namely cardiac mitochondrial proteins. The analysis of GAPDH resulted in the site-specific identification of two AAA and four GGS residues. Computational evaluation of the identified AAS and GGS sites in GAPDH indicated that these sites are located in flexible regions, show high solvent accessibility values, and are in proximity with possible metal ion binding sites. The targeted proteomic analysis of semialdehydic modifications in cardiac mitochondria yielded nine AAS modification sites which were unambiguously assigned to distinct lysine residues in the following proteins: ATP/ATP translocase isoforms 1 and 2, ubiquinol cytochrome-c reductase core protein 2, and ATP synthase α-subunit.

Effect of phenolic compounds on the formation of alpha-aminoadipic and gamma-glutamic semialdehydes from myofibrillar proteins oxidized by copper, iron, and myoglobin

The effect of selected phenolic compounds, namely, gallic acid, chlorogenic acid, genistein, catechin, cyanidin-3-glucoside and rutin, on the formation of specific protein carbonyls, alpha-aminoadipic and gamma-glutamic semialdehydes (AAS and GGS, respectively), from oxidized myofibrillar proteins, was studied in the present article. Suspensions containing myofibrillar proteins (20 mg/mL) and the aforementioned phenolic compounds (1 mM) were oxidized (37 degrees C for 20 days) in the presence of copper acetate, iron (FeCl(3)), or myoglobin (10 microM) in combination with 1 mM H(2)O(2) and analyzed for AAS and GGS using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). Suspensions with added alpha-tocopherol (1 mM) and a control group (with no phenolic compound) were also considered. In the presence of copper, the alpha-tocopherol and most phenolic compounds significantly inhibited the formation of AAS and GGS. In iron- and myoglobin-oxidized suspensions, however, some of those phenolic compounds (i.e., chlorogenic acid and genistein) promoted the formation of the semialdehydes. Besides the influence of the oxidation promoters, the overall effect of plant phenolics on protein oxidation is likely affected by the chemical structure of the phenolics and the result of the interactions between these compounds and myofibrillar proteins. Plausible mechanisms for the antioxidant and pro-oxidant effects of plant phenolics on myofibrillar proteins are proposed in the present article. This study highlights the complexity of redox reactions between plant phenolics and oxidizing myofibrillar proteins.

Tryptophan depletion and formation of alpha-aminoadipic and gamma-glutamic semialdehydes in porcine burger patties with added phenolic-rich fruit extracts

The effect of added fruit extracts on the oxidation of muscle proteins in porcine burger patties subjected to cooking and chill storage was studied. Extracts from arbutus berries (Arbutus unedo L., AU), common hawthorns (Crataegus monogyna L., CM), dog roses (Rosa canina L., RC), and elm-leaf blackberries (Rubus ulmifolius Schott, RU) were prepared, characterized, added to burger patties (3% of total weight), and evaluated as inhibitors of protein oxidation. Negative (no added extract, C) and positive control (added quercetin, 230 mg/kg, Q) groups were also included in the design. Protein oxidation was assessed by means of tryptophan loss using fluorescence spectroscopy (FS) and formation of the specific protein carbonyls alpha-aminoadipic (AAS) and gamma-glutamic semialdehyde (GGS) using liquid chromatography and mass spectroscopy (LC-MS). Both advanced methodologies (FS and LC-MS) were found to be reliable and specific protein oxidation measurements that allow us to gain chemical insight into protein oxidation. The mechanisms likely involved in the oxidative reactions affecting proteins during cooking and storage of burger patties are profusely discussed. Phenolic-rich fruit extracts protected tryptophan residues against oxidation and inhibited the formation of both semialdehydes in burger patties during cooking and subsequent chill storage. In general, RC, RU, and AU were the most effective inhibitors of protein oxidation, with this effect being more intense than that of pure polyphenols like quercetin. These fruit extracts could be considered functional ingredients as their antioxidant actions contribute to the enhancement of the nutritional value of the meat products.

Aldehyde dehydrogenase 7A1 (ALDH7A1) is a novel enzyme involved in cellular defense against hyperosmotic stress

Mammalian ALDH7A1 is homologous to plant ALDH7B1, an enzyme that protects against various forms of stress, such as salinity, dehydration, and osmotic stress. It is known that mutations in the human ALDH7A1 gene cause pyridoxine-dependent and folic acid-responsive seizures. Herein, we show for the first time that human ALDH7A1 protects against hyperosmotic stress by generating osmolytes and metabolizing toxic aldehydes. Human ALDH7A1 expression in Chinese hamster ovary cells attenuated osmotic stress-induced apoptosis caused by increased extracellular concentrations of sucrose or sodium chloride. Purified recombinant ALDH7A1 efficiently metabolized a number of aldehyde substrates, including the osmolyte precursor, betaine aldehyde, lipid peroxidation-derived aldehydes, and the intermediate lysine degradation product, alpha-aminoadipic semialdehyde. The crystal structure for ALDH7A1 supports the enzyme's substrate specificities. Tissue distribution studies in mice showed the highest expression of ALDH7A1 protein in liver, kidney, and brain, followed by pancreas and testes. ALDH7A1 protein was found in the cytosol, nucleus, and mitochondria, making it unique among the aldehyde dehydrogenase enzymes. Analysis of human and mouse cDNA sequences revealed mitochondrial and cytosolic transcripts that are differentially expressed in a tissue-specific manner in mice. In conclusion, ALDH7A1 is a novel aldehyde dehydrogenase expressed in multiple subcellular compartments that protects against hyperosmotic stress by generating osmolytes and metabolizing toxic aldehydes.

Effects of Campomanesia xanthocarpa on biochemical, hematological and oxidative stress parameters in hypercholesterolemic patients

ETHNOPHARMACOLOGICAL RELEVANCE

In Southern Brazil, the plant Campomanesia xanthocarpa Berg. (Myrtaceae), popularly known as "guavirova", has been empirically used for its potential effect in reducing blood cholesterol levels.

AIM OF THE STUDY

Since there are no scientific data confirming its popular use, the aim of the present study was to investigate the effect of Campomanesia xanthocarpa on biochemical, hematological, anthropometrical and oxidative stress parameters in hypercholesterolemic patients.

MATERIALS AND METHODS

Thirty three patients were selected according to total cholesterol (TC) levels: 200-240 mg/dL, undesirable level (UL), and >240 mg/dL, hypercholesterolemic level (HL). UL or HL patients were randomly divided into control group (CG), which received placebo capsules, and experimental group 250 (EG 250) or 500 (EG 500), which received either 250 or 500 mg of encapsulated Campomanesia xanthocarpa. All groups received a cholesterol restriction diet and capsules once a day. The biochemical (TC, triglycerides, HDL, LDL and VLDL), hematological (hematocrit and hemoglobin), anthropometrical (weight and abdominal circumference) and oxidative stress (protein carbonyl) parameters were measured before, 45 and 90 days after the treatment started.

RESULTS

There was no alteration on biochemical, hematological, anthropometric or oxidative stress parameters in UL patients of all groups. However, a significant decrease in TC and LDL levels was observed in HL patients from EG 500 group (reduction of 28+/-3% and 45+/-4% to levels before treatment) in relation to CG group patients (reduction of 12+/-2% and 29+/-4%). Moreover, a significant reduction in oxidative stress was observed in HL patients of EG 250 (51+/-12%) and EG 500 groups (34+/-18%) when compared to levels before treatment. A positive correlation between plasma oxidative stress PC and TC levels was observed. Finally, we found that Campomanesia xanthocarpa extract possesses anti-oxidant properties and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitory activity in vitro.

CONCLUSION

Confirming its popular use, the treatment with Campomanesia xanthocarpa encapsulated reduced blood TC and LDL levels in hypercholesterolemic patients.

Analysis of protein oxidation markers alpha-aminoadipic and gamma-glutamic semialdehydes in food proteins using liquid chromatography (LC)-electrospray ionization (ESI)-multistage tandem mass spectrometry (MS)

To elucidate the formation of protein oxidation biomarkers alpha-aminoadipic semialdehyde (AAS) and gamma-glutamic semialdehyde (GGS) in food proteins was the main purpose of the present study. Food proteins, namely, myofibrillar proteins, alpha-lactalbumin, and soy proteins, as well as bovine serum albumin (BSA), were suspended in a piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES) buffer and oxidized by Fe(3+) and H(2)O(2) while kept in an oven for 14 days at 37 degrees C. For the analysis of semialdehydes, a derivatization procedure with p-aminobenzoic acid (ABA) and NaCNBH(3) followed by liquid chromatography (LC)-electrospray ionization (ESI)-multistage tandem mass spectrometry (MS) was performed. For comparative purposes, the dinitrophenylhydrazine (DNPH) method was also employed as a routine method to assess carbonyl gain. Both semialdehydes were specifically and accurately detected by LC-MS in all oxidized proteins proving that GGS and AAS are formed as a consequence of the oxidation of lysine, proline, and arginine amino acid residues from BSA and other food proteins. Proteins from an animal source and, particularly, BSA were more susceptible to undergo oxidative reactions than soy proteins. The results from the present paper highlight the significance of using both semialdehydes as protein oxidation indicators in meat and dairy products. The analysis of GGS and AAS in real food systems would contribute to the understanding of the precise mechanisms involved in food protein oxidation and shed light on the fate of oxidizing amino acids during food processing and storage.