Adductome-based identification of biomarkers for lipid peroxidation

Multi-adductomics: Advancing mass spectrometry techniques for comprehensive exposome characterization

Adductomics, an emerging field within the 'omics sciences, focuses on the formation and prevalence of DNA, RNA, and protein adducts induced by endogenous and exogenous agents in biological systems. These modifications often result from exposure to environmental pollutants, dietary components, and xenobiotics, impacting cellular functions and potentially leading to diseases such as cancer. This review highlights advances in mass spectrometry (MS) that enhance the detection of these critical modifications and discusses current and emerging trends in adductomics, including developments in MS instrument use, screening techniques, and the study of various biomolecular modifications from mono-adducts to complex hybrid crosslinks between different types of biomolecules. The review also considers challenges, including the need for specialized MS spectra databases and multi-omics integration, while emphasizing techniques to distinguish between exogenous and endogenous modifications. The future of adductomics possesses significant potential for enhancing our understanding of health in relation to environmental exposures and precision medicine.

Analysis of mechanism, therapeutic strategies, and potential natural compounds against atherosclerosis by targeting iron overload-induced oxidative stress

Ferroptosis is a novel form of cell demise characterized primarily by the reduction of trivalent iron to divalent iron, leading to the release of reactive oxygen species (ROS) and consequent induction of intense oxidative stress. In atherosclerosis (AS), highly accumulated lipids are modified by ROS to promote the formation of lipid peroxides, further amplifying cellular oxidative stress damage to influence all stages of atherosclerotic development. Macrophages are regarded as pivotal executors in the progression of AS and the handling of iron, thus targeting macrophage iron metabolism holds significant guiding implications for exploring potential therapeutic strategies against AS. In this comprehensive review, we elucidate the potential interplay among iron overload, inflammation, and lipid dysregulation, summarizing the potential mechanisms underlying the suppression of AS by alleviating iron overload. Furthermore, the application of Traditional Chinese Medicine (TCM) is increasingly widespread. Based on extant research and the pharmacological foundations of active compounds of TCM, we propose alternative therapeutic agents for AS in the context of iron overload, aiming to diversify the therapeutic avenues.

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Recognition of Oxidized Lipids by Macrophages and Its Role in Atherosclerosis Development

Atherosclerosis is a multifactorial chronic disease that has a prominent inflammatory component. Currently, atherosclerosis is regarded as an active autoimmune process that involves both innate and adaptive immune pathways. One of the drivers of this process is the presence of modified low-density lipoprotein (LDL). For instance, lipoprotein oxidation leads to the formation of oxidation-specific epitopes (OSE) that can be recognized by the immune cells. Macrophage response to OSEs is recognized as a key trigger for initiation and a stimulator of progression of the inflammatory process in the arteries. At the same time, the role of oxidized LDL components is not limited to pro-inflammatory stimulation, but includes immunoregulatory effects that can have protective functions. It is, therefore, important to better understand the complexity of oxidized LDL effects in atherosclerosis in order to develop new therapeutic approaches to correct the inflammatory and metabolic imbalance associated with this disorder. In this review, we discuss the process of oxidized LDL formation, mechanisms of OSE recognition by macrophages and the role of these processes in atherosclerosis.

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

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

Inhibition of ferroptosis alleviates atherosclerosis through attenuating lipid peroxidation and endothelial dysfunction in mouse aortic endothelial cell

Atherosclerosis (AS) is the fundamental pathological state of many serious vascular diseases, characterized by disorders of lipid metabolism. Ferroptosis is a type of regulated cell death that is mainly mediated by iron-dependent lipid peroxidation. In this study, whether ferroptosis has occurred in AS and the potential effects of ferroptosis on AS were investigated. Ferroptosis inhibitor ferrostatin-1 (Fer-1) was administered to high-fat diet (HFD)-induced AS in ApoE^-/- mice. The results showed that Fer-1 could alleviate AS lesion in HFD-fed ApoE^-/- mice. Additionally, Fer-1 partially inhibited the iron accumulation, lipid peroxidation and reversed the expressions of ferroptosis indicators SLC7A11 and glutathione peroxidase 4 (GPX4) in HFD-fed ApoE^-/- mice. Next, we evaluated the effects of inhibition of ferroptosis on oxidized-low density lipoprotein (ox-LDL)-induced mouse aortic endothelial cells (MAECs). Results showed that Fer-1 increased cell viability and reduced cell death in ox-LDL-treated MAECs. Moreover, Fer-1 decreased iron content and lipid peroxidation and up-regulated the levels of SLC7A11 and GPX4. Additionally, Fer-1 down-regulated the expressions of adhesion molecules and up-regulated eNOS expression. Iron chelator deferoxamine was used to demonstrate ferroptosis could be partially inhibited by iron complexation in ox-LDL-treated MAECs. Our results indicated that ferroptosis might occur during the initiation and development of AS. More importantly, inhibition of ferroptosis could alleviate AS through attenuating lipid peroxidation and endothelial dysfunction in AECs. Our findings might contribute to a deeper understanding regarding the pathological process of AS and provide a therapeutic target for AS.

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.

Epitope mapping and characterization of 4-hydroxy-2-nonenal modified-human serum albumin using two different polyclonal antibodies

Lipids are susceptible to damage by reactive oxygen species, and from lipid oxidation reactions many short chain lipid peroxidation products can be formed. 4-Hydroxy-2-nonenal (HNE) is one of the most abundant and cytotoxic lipid oxidation products and is known to form covalent adducts with nucleophilic amino acids of proteins. HNE-modified proteins have value as biomarkers and can be detected by antibody-based techniques, but most commercially available antibodies were raised against HNE-keyhole limpet hemocyanin. We used HNE-treated human serum albumin (HSA) to raise sheep antiserum and report for the first time the use of covalently modified peptide arrays to assess epitope binding of antibodies (Abs). Peptide arrays covering the sequence of HSA and treated post peptide synthesis with HNE were used to compare the different binding patterns of a commercial polyclonal antibody (pAb) raised against HNE-treated KLH and an in-house anti-HNE enriched pAb. The results were correlated with analysis of HNE-modified HSA by high-resolution tandem mass spectrometry. Both anti-HNE pAbs were found to bind strongly to eight common peptides on the HNE-treated HSA membranes, suggesting that HNE adducts per se induced an immune response in both cases even though different immunogens were used. Both antibodies bound with the highest affinity to the peptide ³⁶⁵DPHECYAKVFDEFKPLV³⁸¹, which contains K378 and was also shown to be modified by the mass spectrometry analysis. Overall, the commercial anti-HNE pAb showed better specificity, recognizing nine out of the eleven adducts found by MS/MS, while the in-house enriched pAb only recognizes six. Nevertheless, the in-house pAb recognized specific peptides that were not recognized by the commercial pAb, which suggests the presence of clones uniquely specific to HNE adducts on HSA.

Protein adductomics: A comprehensive analysis of protein modifications by electrophiles

Human individuals are continually exposed to various exogenous and endogenous reactive electrophiles, which readily react with nucleophilic biomacromolecules, such as protein, and form a variety of covalent adducts. The covalent modifications of protein are thought to be involved in various physiological and pathological processes. Recently, the "adductome", a new concept that represents the totality of covalent adducts bound to nucleophilic biomolecules, has been offered as a useful technique for characterizing essentially all reactive electrophilic compounds in biological samples. The primary advantage of this approach is that non-targeted comprehensive analysis can readily be extended to investigate covalent adduct pattern of different situation of exposure and thereby makes it possible to detect/identify not only known but also unknown adducts. In this review, we provide a summary of the concept and methodology of protein adductomics, especially focusing on redox protein adductomics.

The Significance of Oxidized Low-Density Lipoprotein in Body Fluids as a Marker Related to Diseased Conditions

Oxidatively modified low-density lipoprotein (oxLDL) is known to be involved in various diseases, including cardiovascular diseases. The presence of oxLDL in the human circulatory system and in atherosclerotic lesions has been demonstrated using monoclonal antibodies. Studies have shown the significance of circulating oxLDL in various systemic diseases, including acute myocardial infarction and diabetic mellitus. Several different enzyme-linked immunosorbent assay (ELISA) procedures to measure oxLDL were utilized. Evidence has been accumulating that reveals changes in oxLDL levels under certain pathological conditions. Since oxLDL concentration tends to correlate with low-density lipoprotein (LDL)-cholesterol, the ratio of ox-LDL and LDL rather than oxLDL concentration alone has also been focused. In addition to circulating plasma, LDL and oxLDL are found in gingival crevicular fluid (GCF), where the ratio of oxLDL to LDL in GCF is much higher than in plasma. LDL and oxLDL levels in GCF show an increase in diabetic patients and periodontal patients, suggesting that GCF might be useful in examining systemic conditions. GCF oxLDL increased when the teeth were affected by periodontitis. It is likely that oxLDL levels in plasma and GCF could reflect oxidative stress and transfer efficacy in the circulatory system.

Protein Adductomics: Analytical Developments and Applications in Human Biomonitoring

Proteins contain many sites that are subject to modification by electrophiles. Detection and characterisation of these modifications can give insights into environmental agents and endogenous processes that may be contributing factors to chronic human diseases. An untargeted approach, utilising mass spectrometry to detect modified amino acids or peptides, has been applied to blood proteins haemoglobin and albumin, focusing in particular on the N-terminal valine residue of haemoglobin and the cysteine-34 residue in albumin. Technical developments to firstly detect simultaneously multiple adducts at these sites and then subsequently to identify them are reviewed here. Recent studies in which the methods have been applied to biomonitoring human exposure to environmental toxicants are described. With advances in sensitivity, high-throughput handling of samples and robust quality control, these methods have considerable potential for identifying causes of human chronic disease and of identifying individuals at risk.

Mass Spectrometry-Based Methodologies for Targeted and Untargeted Identification of Protein Covalent Adducts (Adductomics): Current Status and Challenges

Protein covalent adducts formed upon exposure to reactive (mainly electrophilic) chemicals may lead to the development of a wide range of deleterious health outcomes. Therefore, the identification of protein covalent adducts constitutes a huge opportunity for a better understanding of events underlying diseases and for the development of biomarkers which may constitute effective tools for disease diagnosis/prognosis, for the application of personalized medicine approaches and for accurately assessing human exposure to chemical toxicants. The currently available mass spectrometry (MS)-based methodologies, are clearly the most suitable for the analysis of protein covalent modifications, providing accuracy, sensitivity, unbiased identification of the modified residue and conjugates along with quantitative information. However, despite the huge technological advances in MS instrumentation and bioinformatics tools, the identification of low abundant protein covalent adducts is still challenging. This review is aimed at summarizing the MS-based methodologies currently used for the identification of protein covalent adducts and the strategies developed to overcome the analytical challenges, involving not only sample pre-treatment procedures but also distinct MS and data analysis approaches.

Lipoxidation in cardiovascular diseases

Lipids can go through lipid peroxidation, an endogenous chain reaction that consists in the oxidative degradation of lipids leading to the generation of a wide variety of highly reactive carbonyl species (RCS), such as short-chain carbonyl derivatives and oxidized truncated phospholipids. RCS exert a wide range of biological effects due to their ability to interact and covalently bind to nucleophilic groups on other macromolecules, such as nucleic acids, phospholipids, and proteins, forming reversible and/or irreversible modifications and generating the so-called advanced lipoxidation end-products (ALEs). Lipoxidation plays a relevant role in the onset of cardiovascular diseases (CVD), mainly in the atherosclerosis-based diseases in which oxidized lipids and their adducts have been extensively characterized and associated with several processes responsible for the onset and development of atherosclerosis, such as endothelial dysfunction and inflammation. Herein we will review the current knowledge on the sources of lipids that undergo oxidation in the context of cardiovascular diseases, both from the bloodstream and tissues, and the methods for detection, characterization, and quantitation of their oxidative products and protein adducts. Moreover, lipoxidation and ALEs have been associated with many oxidative-based diseases, including CVD, not only as potential biomarkers but also as therapeutic targets. Indeed, several therapeutic strategies, acting at different levels of the ALEs cascade, have been proposed, essentially blocking ALEs formation, but also their catabolism or the resulting biological responses they induce. However, a deeper understanding of the mechanisms of formation and targets of ALEs could expand the available therapeutic strategies.

2-Alkenal modification of hemoglobin: Identification of a novel hemoglobin-specific alkanoic acid-histidine adduct

α,β-Unsaturated aldehydes generated during lipid peroxidation, such as 2-alkenals, give rise to protein degeneration in a variety of pathological states. 2-Alkenals are highly reactive toward nucleophilic amino acid residues, such as histidine and lysine, to form Schiff base adducts or Michael addition adducts. In this study, upon the reaction of hemoglobin with 2-octenal, we unexpectedly detected a product corresponding to the reduced form of the 2-octenal-histidine Michael adduct plus 14 mass unit. Based on the LC-ESI-MS/MS analysis of synthetic adduct candidates, the adduct was identified to be N^τ-(1-carboxyheptan-2-yl)-histidine (CHH), a novel alkanoic acid-type histidine adduct. The alkanoic acid-histidine adducts were detected in the 2-alkenal-treated hemoglobin and myoglobin, but not in the 2-alkenal-treated cytochrome c and transferrin. The addition of hemin to the reaction mixture, containing a non-heme protein and 2-alkenals, resulted in the formation of the alkanoic acid-histidine adducts, suggesting that a heme iron may play a role in the oxidation of covalently modified proteins. Moreover, using the stable isotope dilution method, we showed evidence for the endogenous formation of CHH in red blood cells exposed to hydrogen peroxide. Thus, this study establishes a novel mechanism for covalent modification of proteins by 2-alkenals, in which heme iron is involved in the formation of the alkanoic acid-histidine adducts. The potential implications of this novel adduct are discussed.

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2-Alkenal-treated hemoglobin was subjected to a comprehensive analysis of the modified histidine.

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The alkanoic acid-type histidine adducts were identified as novel adducts formed in the 2-alkenal-modified hemoglobin.

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This type of adducts was suggested to be formed by the iron-dependent oxidation of 2-alkenal-histidine Michael adducts.

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The alkanoic acid-type histidine adducts were generated in red blood cells exposed to H₂O₂.

Lipoproteins as targets and markers of lipoxidation

Lipoproteins are essential systemic lipid transport particles, composed of apolipoproteins embedded in a phospholipid and cholesterol monolayer surrounding a cargo of diverse lipid species. Many of the lipids present are susceptible to oxidative damage by lipid peroxidation, giving rise to the formation of reactive lipid peroxidation products (rLPPs). In view of the close proximity of the protein and lipid moieties within lipoproteins, the probability of adduct formation between rLPPs and amino acid residues of the proteins, a process called lipoxidation, is high. There has been interest for many years in the biological effects of such modifications, but the field has been limited to some extent by the availability of methods to determine the sites and exact nature of such modification. More recently, the availability of a wide range of antibodies to lipoxidation products, as well as advances in analytical techniques such as liquid chromatography tandem mass spectrometry (LC-MSMS), have increased our knowledge substantially. While most work has focused on LDL, oxidation of which has long been associated with pro-inflammatory responses and atherosclerosis, some studies on HDL, VLDL and Lipoprotein(a) have also been reported. As the broader topic of LDL oxidation has been reviewed previously, this review focuses on lipoxidative modifications of lipoproteins, from the historical background through to recent advances in the field. We consider the main methods of analysis for detecting rLPP adducts on apolipoproteins, including their advantages and disadvantages, as well as the biological effects of lipoxidized lipoproteins and their potential roles in diseases.

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Lipoproteins can be modified by reactive Lipid Peroxidation Products (rLPPs).

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Lipoprotein lipoxidation is known to occur in several inflammatory diseases.

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Biochemical, immunochemical and mass spectrometry methods can detect rLPP adducts.

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Due to higher information output, MS can facilitate localization of modifications.

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Antibodies against some rLPPs have been used to identify lipoxidation in vivo.

Cholesterol secosterol aldehyde adduction and aggregation of Cu,Zn-superoxide dismutase: Potential implications in ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by degeneration of upper and lower motor neurons. While the fundamental causes of the disease are still unclear, the accumulation of Cu,Zn-superoxide dismutase (SOD1) immunoreactive aggregates is associated with familial ALS cases. Cholesterol 5,6-secosterol aldehydes (Seco A and Seco B) are reported to contribute to neurodegenerative disease pathology by inducing protein modification and aggregation. Here we have investigated the presence of secosterol aldehydes in ALS SOD1-G93A rats and their capacity to induce SOD1 aggregation. Secosterol aldehydes were analyzed in blood plasma, spinal cord and motor cortex of ALS rats at the pre-symptomatic and symptomatic stages. Seco B was significantly increased in plasma of symptomatic ALS rats compared to pre-symptomatic animals, suggesting an association with disease progression. In vitro experiments showed that both Seco A and Seco B induce the formation of high molecular weight (HMW) SOD1 aggregates with amorphous morphology. SOD1 adduction to ω-alkynyl-secosterols analyzed by click assay showed that modified proteins are only detected in the HMW region, indicating that secosterol adduction generates species highly prone to aggregate. Of note, SOD1-secosterol adducts containing up to five secosterol molecules were confirmed by MALDI-TOF analysis. Interestingly, mass spectrometry sequencing of SOD1 aggregates revealed preferential secosterol adduction to Lys residues located at the electrostatic loop (Lys 122, 128 and 136) and nearby the dimer interface (Lys 3 and 9). Altogether, our results show that secosterol aldehydes are increased in plasma of symptomatic ALS rats and represent a class of aldehydes that can potentially modify SOD1 enhancing its propensity to aggregate.

Lipid (per) oxidation in mitochondria: an emerging target in the ageing process?

Lipids are essential for physiological processes such as maintaining membrane integrity, providing a source of energy and acting as signalling molecules to control processes including cell proliferation, metabolism, inflammation and apoptosis. Disruption of lipid homeostasis can promote pathological changes that contribute towards biological ageing and age-related diseases. Several age-related diseases have been associated with altered lipid metabolism and an elevation in highly damaging lipid peroxidation products; the latter has been ascribed, at least in part, to mitochondrial dysfunction and elevated ROS formation. In addition, senescent cells, which are known to contribute significantly to age-related pathologies, are also associated with impaired mitochondrial function and changes in lipid metabolism. Therapeutic targeting of dysfunctional mitochondrial and pathological lipid metabolism is an emerging strategy for alleviating their negative impact during ageing and the progression to age-related diseases. Such therapies could include the use of drugs that prevent mitochondrial uncoupling, inhibit inflammatory lipid synthesis, modulate lipid transport or storage, reduce mitochondrial oxidative stress and eliminate senescent cells from tissues. In this review, we provide an overview of lipid structure and function, with emphasis on mitochondrial lipids and their potential for therapeutic targeting during ageing and age-related disease.

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.