Low Levels of IgM Recognizing 4-Hydroxy-2-Nonenal-Modified Apolipoprotein A-I Peptide and Its Association with the Severity of Coronary Artery Disease in Taiwanese Patients

Autoantibodies against apolipoprotein A-I (ApoA-I) are associated with cardiovascular disease risks. We aimed to examine the 4-hydroxy-2-nonenal (HNE) modification of ApoA-I in coronary artery disease (CAD) and evaluate the potential risk of autoantibodies against their unmodified and HNE-modified peptides. We assessed plasma levels of ApoA-I, HNE-protein adducts, and autoantibodies against unmodified and HNE-peptide adducts, and significant correlations and odds ratios (ORs) were examined. Two novel CAD-specific HNE-peptide adducts, ApoA-I251-262 and ApoA-I70-83, were identified. Notably, immunoglobulin G (IgG) anti-ApoA-I251-262 HNE, IgM anti-ApoA-I70-83 HNE, IgG anti-ApoA-I251-262, IgG anti-ApoA-I70-83, and HNE-protein adducts were significantly correlated with triglycerides, creatinine, or high-density lipoprotein in CAD with various degrees of stenosis (<30% or >70%). The HNE-protein adduct (OR = 2.208-fold, p = 0.020) and IgM anti-ApoA-I251-262 HNE (2.046-fold, p = 0.035) showed an increased risk of progression from >30% stenosis in CAD. HNE-protein adducts and IgM anti-ApoA-I251-262 HNE may increase the severity of CAD at high and low levels, respectively.

Unveiling Atherosclerotic Plaque Heterogeneity and SPP1+/VCAN+ Macrophage Subtype Prognostic Significance Through Integrative Single-Cell and Bulk-Seq Analysis

Background

Dysregulated macrophages are important causes of Atherosclerosis (AS) formation and increased plaque instability, but the heterogeneity of these plaques and the role of macrophage subtypes in plaque instability have yet to be clarified.

Methods

This study integrates single-cell and bulk-seq data to analyze atherosclerotic plaques. Unsupervised clustering was used to reveal distinct plaque subtypes, while survival analysis and gene set variation analysis (GSVA) methods helped in understanding their clinical outcomes. Enrichment of differential expression of macrophage genes (DEMGs) score and pseudo-trajectory analysis were utilized to explore the biological functions and differentiation stages of macrophage subtypes in AS progression. Additionally, CellChat and the BayesPrism deconvolution method were used to elucidate macrophage subtype interaction and their prognostic significance at single-cell resolution. Finally, the expression of biomarkers was validated in mouse experiments.

Results

Three distinct AS plaque subtypes were identified, with cluster 3 plaque subtype being particularly associated with higher immune infiltration and poorer prognosis. The DEMGs score exhibited a significant elevation in three macrophage subtypes (SPP1+/VCAN+ macrophages, IL1B+ macrophages, and FLT3LG+ macrophages), associated with cluster 3 plaque subtype and highlighted the prognostic significance of these subtypes. Activation trajectory of the macrophage subtypes is divided into three states (Pre-branch, Cell fate 1, and Cell fate 2), and Cell fate 2 (SPP1+/VCAN+ macrophages, IL1B+ macrophages, and FLT3LG+ macrophages dominant) exhibiting the highest DEMGs score, distinct interactions with other cell components, and relating to poorer prognosis of ischemic events. This study also uncovered a unique SPP1+/VCAN+ macrophage subtype, rare in quantity but significant in influencing AS progression. Machine learning algorithms identified 10 biomarkers crucial for AS diagnosis. The validation of these biomarkers was performed using Mendelian Randomization analysis and in vitro methods, supporting their relevance in AS pathology.

Conclusion

Our study provides a comprehensive view of AS plaque heterogeneity and the prognostic significance of macrophage subtypes in plaque instability.

The 4-Hydroxynonenal–Protein Adducts and Their Biological Relevance: Are Some Proteins Preferred Targets?

It is well known that oxidative stress and lipid peroxidation (LPO) play a role in physiology and pathology. The most studied LPO product with pleiotropic capabilities is 4-hydroxynonenal (4-HNE). It is considered as an important mediator of cellular signaling processes and a second messenger of reactive oxygen species. The effects of 4-HNE are mainly attributed to its adduction with proteins. Whereas the Michael adducts thus formed are preferred in an order of potency of cysteine > histidine > lysine over Schiff base formation, it is not known which proteins are the preferred targets for 4-HNE under what physiological or pathological conditions. In this review, we briefly discuss the methods used to identify 4-HNE–protein adducts, the progress of mass spectrometry in deciphering the specific protein targets, and their biological relevance, focusing on the role of 4-HNE protein adducts in the adaptive response through modulation of the NRF2/KEAP1 pathway and ferroptosis.

Novel Insights Into Sterol Uptake and Intracellular Cholesterol Trafficking During Eimeria bovis Macromeront Formation

Apicomplexan parasites are considered as defective in cholesterol synthesis. Consequently, they need to scavenge cholesterol from the host cell by either enhancing the uptake of extracellular cholesterol sources or by upregulating host cellular de-novo biosynthesis. Given that Eimeria bovis macromeront formation in bovine lymphatic endothelial host cells in vivo is a highly cholesterol-demanding process, we here examined host parasite interactions based on host cellular uptake of different low-density lipoprotein (LDL) types, i.e., of non-modified (LDL), oxidized (oxLDL), and acetylated LDL (acLDL). Furthermore, the expression of lipoprotein-oxidized receptor 1 (LOX-1), which mediates acLDL and oxLDL internalization, was monitored throughout first merogony, in vitro and ex vivo. Moreover, the effects of inhibitors blocking exogenous sterol uptake or intracellular transport were studied during E. bovis macromeront formation in vitro. Hence, E. bovis-infected primary bovine umbilical vein endothelial cells (BUVEC) were treated with inhibitors of sterol uptake (ezetimibe, poly-C, poly-I, sucrose) and of intracellular sterol transport and release from endosomes (progesterone, U18666A). As a read-out system, the size and number of macromeronts as well as merozoite I production were estimated. Overall, the internalization of all LDL modifications (LDL, oxLDL, acLDL) was observed in E. bovis-infected BUVEC but to different extents. Supplementation with oxLDL and acLDL at lower concentrations (5 and 10 µg/ml, respectively) resulted in a slight increase of both macromeront numbers and size; however, at higher concentrations (25–50 µg/ml), merozoite I production was diminished. LOX-1 expression was enhanced in E. bovis-infected BUVEC, especially toward the end of merogony. As an interesting finding, ezetimibe treatments led to a highly significant blockage of macromeront development and merozoite I production confirming the relevance of sterol uptake for intracellular parasite development. Less prominent effects were induced by non-specific inhibition of LDL internalization via sucrose, poly-I, and poly-C. In addition, blockage of cholesterol transport via progesterone and U18666A treatments resulted in significant inhibition of parasite development. Overall, current data underline the relevance of exogenous sterol uptake and intracellular cholesterol transport for adequate E. bovis macromeront development, unfolding new perspectives for novel drug targets against E. bovis.

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.

Isotypes of autoantibodies against novel differential 4-hydroxy-2-nonenal-modified peptide adducts in serum is associated with rheumatoid arthritis in Taiwanese women

Background

Rheumatoid arthritis (RA) is an autoimmune disorder with systemic inflammation and may be induced by oxidative stress that affects an inflamed joint. Our objectives were to examine isotypes of autoantibodies against 4-hydroxy-2-nonenal (HNE) modifications in RA and associate them with increased levels of autoantibodies in RA patients.

Methods

Serum samples from 155 female patients [60 with RA, 35 with osteoarthritis (OA), and 60 healthy controls (HCs)] were obtained. Four novel differential HNE-modified peptide adducts, complement factor H (CFAH)^1211–1230, haptoglobin (HPT)^78–108, immunoglobulin (Ig) kappa chain C region (IGKC)^2–19, and prothrombin (THRB)^328–345, were re-analyzed using tandem mass spectrometric (MS/MS) spectra (ProteomeXchange: PXD004546) from RA patients vs. HCs. Further, we determined serum protein levels of CFAH, HPT, IGKC and THRB, HNE-protein adducts, and autoantibodies against unmodified and HNE-modified peptides. Significant correlations and odds ratios (ORs) were calculated.

Results

Levels of HPT in RA patients were greatly higher than the levels in HCs. Levels of HNE-protein adducts and autoantibodies in RA patients were significantly greater than those of HCs. IgM anti-HPT⁷⁸⁻¹⁰⁸ HNE, IgM anti-IGKC²⁻¹⁹, and IgM anti-IGKC²⁻¹⁹ HNE may be considered as diagnostic biomarkers for RA. Importantly, elevated levels of IgM anti-HPT⁷⁸⁻¹⁰⁸ HNE, IgM anti-IGKC²⁻¹⁹, and IgG anti-THRB^328−345 were positively correlated with the disease activity score in 28 joints for C-reactive protein (DAS28-CRP). Further, the ORs of RA development through IgM anti-HPT⁷⁸⁻¹⁰⁸ HNE (OR 5.235, p < 0.001), IgM anti-IGKC²⁻¹⁹ (OR 12.655, p < 0.001), and IgG anti-THRB^328−345 (OR 5.761, p < 0.001) showed an increased risk. Lastly, we incorporated three machine learning models to differentiate RA from HC and OA, and performed feature selection to determine discriminative features. Experimental results showed that our proposed method achieved an area under the receiver operating characteristic curve of 0.92, which demonstrated that our selected autoantibodies combined with machine learning can efficiently detect RA.

Conclusions

This study discovered that some IgG- and IgM-NAAs and anti-HNE M-NAAs may be correlated with inflammation and disease activity in RA. Moreover, our findings suggested that IgM anti-HPT⁷⁸⁻¹⁰⁸ HNE, IgM anti-IGKC²⁻¹⁹, and IgG anti-THRB^328−345 may play heavy roles in RA development.

Oxidation specific epitopes in asthma: New possibilities for treatment

Oxidative stress is an important feature of asthma pathophysiology that is not currently targeted by any of our frontline treatments. Reactive oxygen species, generated during times of heightened oxidative stress, can damage cellular lipids causing the production of oxidation specific epitopes (OSE). OSEs are elevated in chronic inflammatory diseases and promoting their clearance by the body, through pattern recognition receptors and IgM antibodies, prevents and resolves inflammation and tissue damage in animal models. Current research on OSEs in asthma is limited. Although they are present in the lungs of people with asthma during periods of exacerbation or allergen exposure, we do not know if they are linked with disease pathobiology. This article reviews our current understanding of OSEs in asthma and explores whether targeting OSE clearance mechanisms may be a novel therapeutic intervention for asthma.

Modified sites and functional consequences of 4-oxo-2-nonenal adducts in HDL that are elevated in familial hypercholesterolemia

The lipid aldehyde 4-oxo-2-nonenal (ONE) is a highly reactive protein crosslinker derived from peroxidation of n-6 polyunsaturated fatty acids and generated together with 4-hydroxynonenal (HNE). Lipid peroxidation product-mediated crosslinking of proteins in high-density lipoprotein (HDL) causes HDL dysfunction and contributes to atherogenesis. Although HNE is relatively well-studied, the role of ONE in atherosclerosis and in modifying HDL is unknown. Here, we found that individuals with familial hypercholesterolemia (FH) had significantly higher ONE-ketoamide (lysine) adducts in HDL (54.6 ± 33.8 pmol/mg) than healthy controls (15.3 ± 5.6 pmol/mg). ONE crosslinked apolipoprotein A-I (apoA-I) on HDL at a concentration of > 3 mol ONE per 10 mol apoA-I (0.3 eq), which was 100-fold lower than HNE, but comparable to the potent protein crosslinker isolevuglandin. ONE-modified HDL partially inhibited HDL's ability to protect against lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) and interleukin-1β (IL-1β) gene expression in murine macrophages. At 3 eq, ONE dramatically decreased apoA-I exchange from HDL, from ∼46.5 to ∼18.4% (p < 0.001). Surprisingly, ONE modification of HDL or apoA-I did not alter macrophage cholesterol efflux capacity. LC-MS/MS analysis revealed that Lys-12, Lys-23, Lys-96, and Lys-226 in apoA-I are modified by ONE ketoamide adducts. Compared with other dicarbonyl scavengers, pentylpyridoxamine (PPM) most efficaciously blocked ONE-induced protein crosslinking in HDL and also prevented HDL dysfunction in an in vitro model of inflammation. Our findings show that ONE-HDL adducts cause HDL dysfunction and are elevated in individuals with FH who have severe hypercholesterolemia.

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.

Besnoitia besnoiti infection alters both endogenous cholesterol de novo synthesis and exogenous LDL uptake in host endothelial cells

Besnoitia besnoiti, an apicomplexan parasite of cattle being considered as emergent in Europe, replicates fast in host endothelial cells during acute infection and is in considerable need for energy, lipids and other building blocks for offspring formation. Apicomplexa are generally considered as defective in cholesterol synthesis and have to scavenge cholesterol from their host cells for successful replication. Therefore, we here analysed the influence of B. besnoiti on host cellular endogenous cholesterol synthesis and on sterol uptake from exogenous sources. GC-MS-based profiling of cholesterol-related sterols revealed enhanced cholesterol synthesis rates in B. besnoiti-infected cells. Accordingly, lovastatin and zaragozic acid treatments diminished tachyzoite production.  Moreover, increased lipid droplet contents and enhanced cholesterol esterification was detected and inhibition of the latter significantly blocked parasite proliferation. Furthermore, artificial increase of host cellular lipid droplet disposability boosted parasite proliferation. Interestingly, lectin-like oxidized low density lipoprotein receptor 1 expression was upregulated in infected endothelial hostcells, whilst low density lipoproteins (LDL) receptor was not affected by parasite infection. However, exogenous supplementations with non-modified and acetylated LDL both boosted B. besnoiti proliferation. Overall, current data show that B. besnoiti simultaneously exploits both, endogenous cholesterol biosynthesis and cholesterol uptake from exogenous sources, during asexual replication.

Protamine may have anti-atherogenic potential by inhibiting the binding of oxidized-low density lipoprotein to LOX-1

Oxidized low-density lipoprotein (ox-LDL) leads to atherosclerosis via lectin-like oxidized lipoprotein receptor-1 (LOX-1), one of the major receptor for ox-LDL. Inhibition of the binding of ox-LDL to LOX-1 decreases the proinflammatory and atherosclerotic events. The aim of the present study was to investigate whether protamine, a polybasic nuclear protein, interferes the binding of ox-LDL to LOX-1. Using sandwich ELISA with newly generated antibody, we measured the blocking effect of protamine on the binding of ox-LDL to LOX-1. Protamine dose-dependently inhibited the binding of ox-LDL to LOX-1. DiI-labeled ox-LDL uptake assay in two types of cultured human endothelial cells was performed with fluorescence microplate reader. Activation of extracellular-signal-regulated kinase (ERK)1/2 by ox-LDL was analyzed by immunoblotting. We found that protamine suppressed uptake of ox-LDL in endothelial cells and inhibited ERK1/2 activation by ox-LDL. These results suggest that protamine may possess anti-atherogenic potential by inhibiting ox-LDL binding to LOX-1 through electrostatic interactions.

Contribution of lectin-like oxidized low-density lipoprotein receptor-1 and LOX-1 modulating compounds to vascular diseases

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is the major receptor for binding and uptake of oxidized low-density lipoprotein (oxLDL) in endothelial cells. LOX-1 is also expressed in macrophages, smooth muscle cells and platelets. Following internalization of oxLDL, LOX-1 initiates a vicious cycle from activation of pro-inflammatory signaling pathways, thus promoting an increased reactive oxygen species formation and secretion of pro-inflammatory cytokines. LOX-1 plays a pivotal role in the development of endothelial dysfunction, foam cell and advanced lesions formation as well as in myocardial ischemia. Furthermore, it is known that LOX-1 plays a pivotal role in mitochondrial DNA damage, vascular cell apoptosis, and autophagy. A large number of studies provide evidence of a LOX-1's role in endothelial dysfunction, hypertension, diabetes, and obesity. In addition, novel insights into LOX-1 ligands and the activated signaling pathways have been gained. Recent studies have shown an interaction of LOX-1 with microRNA's, thus providing novel tools to regulate LOX-1 function. Because LOX-1 is increased in atherosclerotic plaques and contributes to endothelial dysfunction, several compounds were tested in vivo and in vitro to modulate the LOX-1 expression in therapeutic approaches.

4-Hydroxynonenal (HNE) modified proteins in metabolic diseases

4-Hydroxynonenal (HNE) is one of the quantitatively most important products of lipid peroxidation. Due to its high toxicity it is quickly metabolized, however, a small share of HNE avoids enzymatic detoxification and reacts with biomolecules including proteins. The formation of HNE-protein-adducts is one of the accompanying processes in oxidative stress or redox disbalance. The modification of proteins might occur at several amino acids side chains, leading to a variety of products and having effects on the protein function and fate. This review summarizes current knowledge on the formation of HNE-modified proteins, their fate in mammalian cells and their potential role as a damaging agents during oxidative stress. Furthermore, the potential of HNE-modified proteins as biomarkers for several diseases are highlighted.

Adductome-based identification of biomarkers for lipid peroxidation

Lipid peroxidation is an endogenous source of aldehydes that gives rise to covalent modification of proteins in various pathophysiological states. In this study, a strategy for the comprehensive detection and comparison of adducts was applied to find a biomarker for lipid peroxidation-modified proteins in vivo This adductome approach utilized liquid chromatography with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) methods designed to detect the specific product ions from positively ionized adducts in a selected reaction monitoring mode. Using this procedure, we comprehensively analyzed lysine and histidine adducts generated in the in vitro oxidized low-density lipoproteins (LDL) and observed a prominent increase in several adducts, including a major lysine adduct. Based on the high resolution ESI-MS of the adduct and on the LC-ESI-MS/MS analysis of the synthetic adduct candidates, the major lysine adduct detected in the oxidized LDL was identified as N^ϵ-(8-carboxyoctanyl)lysine (COL). Strikingly, a significantly higher amount of COL was detected in the sera from atherosclerosis-prone mice and from patients with hyperlipidemia compared with the controls. These data not only offer structural insights into protein modification by lipid peroxidation products but also provide a platform for the discovery of biomarkers for human diseases.

Roles of Vascular Oxidative Stress and Nitric Oxide in the Pathogenesis of Atherosclerosis

Major reactive oxygen species (ROS)–producing systems in vascular wall include NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase, xanthine oxidase, the mitochondrial electron transport chain, and uncoupled endothelial nitric oxide (NO) synthase. ROS at moderate concentrations have important signaling roles under physiological conditions. Excessive or sustained ROS production, however, when exceeding the available antioxidant defense systems, leads to oxidative stress. Animal studies have provided compelling evidence demonstrating the roles of vascular oxidative stress and NO in atherosclerosis. All established cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, and smoking enhance ROS generation and decrease endothelial NO production. Key molecular events in atherogenesis such as oxidative modification of lipoproteins and phospholipids, endothelial cell activation, and macrophage infiltration/activation are facilitated by vascular oxidative stress and inhibited by endothelial NO. Atherosclerosis develops preferentially in vascular regions with disturbed blood flow (arches, branches, and bifurcations). The fact that these sites are associated with enhanced oxidative stress and reduced endothelial NO production is a further indication for the roles of ROS and NO in atherosclerosis. Therefore, prevention of vascular oxidative stress and improvement of endothelial NO production represent reasonable therapeutic strategies in addition to the treatment of established risk factors (hypercholesterolemia, hypertension, and diabetes mellitus).

Innate sensing of oxidation-specific epitopes in health and disease

Ageing, infections and inflammation result in oxidative stress that can irreversibly damage cellular structures. The oxidative damage of lipids in membranes or lipoproteins is one of these deleterious consequences that not only alters lipid function but also leads to the formation of neo-self epitopes - oxidation-specific epitopes (OSEs) - which are present on dying cells and damaged proteins. OSEs represent endogenous damage-associated molecular patterns that are recognized by pattern recognition receptors and the proteins of the innate immune system, and thereby enable the host to sense and remove dangerous biological waste and to maintain homeostasis. If this system is dysfunctional or overwhelmed, the accumulation of OSEs can trigger chronic inflammation and the development of diseases, such as atherosclerosis and age-related macular degeneration. Understanding the molecular components and mechanisms that are involved in this process will help to identify individuals with an increased risk of developing chronic inflammation, and will also help to indicate novel modes of therapeutic intervention.

Malondialdehyde epitopes as mediators of sterile inflammation

Enhanced lipid peroxidation occurs during oxidative stress and results in the generation of lipid peroxidation end products such as malondialdehyde (MDA), which can attach to autologous biomolecules, thereby generating neo-self epitopes capable of inducing potentially undesired biological responses. Therefore, the immune system has developed mechanisms to protect from MDA epitopes by binding and neutralizing them through both cellular and soluble effectors. Here, we briefly discuss innate immune responses targeting MDA epitopes and their pro-inflammatory properties, followed by a review of physiological carriers of MDA epitopes that are relevant in homeostasis and disease. Then we discuss in detail the evidence for cellular responses towards MDA epitopes mainly in lung, liver and the circulation as well as signal transduction mechanisms and receptors implicated in the response to MDA epitopes. Last, we hypothesize on the role of MDA epitopes as mediators of inflammation in diseases and speculate on their contribution to disease pathogenesis. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

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.

Oxidative theory of atherosclerosis and antioxidants

Atherosclerosis is a multifactorial process that begins early in infancy and affects all the humans. Early steps of atherogenesis and the evolution towards complex atherosclerotic plaques are briefly described. After a brief history of the 'Lipid theory of atherosclerosis', we report the most prominent discoveries on lipoproteins, their receptors and metabolism, and their role in atherogenesis. The main focus is the 'oxidative theory of atherosclerosis', with emphasis on free radicals and reactive oxygen species, lipid peroxidation and LDL oxidation, biological properties of oxidized LDL and their potential role in atherogenesis. Then, we report the properties of antioxidants and antioxidant systems and their effects in vitro, on cultured cells, in animal models and in humans. The surprising discrepancy between the efficacy of antioxidants in vitro and in animal models of atherosclerosis and the lack of protective effect against cardiovascular events and death in epidemiological study and clinical trials are discussed. In contrast, epidemiological studies seem to indicate that the Mediterranean diet may protect (in part) against atherosclerosis complications (myocardial infarction and cardiovascular death).

4-Hydroxy-nonenal-A Bioactive Lipid Peroxidation Product

This review on recent research advances of the lipid peroxidation product 4-hydroxy-nonenal (HNE) has four major topics: I. the formation of HNE in various organs and tissues, II. the diverse biochemical reactions with Michael adduct formation as the most prominent one, III. the endogenous targets of HNE, primarily peptides and proteins (here the mechanisms of covalent adduct formation are described and the (patho-) physiological consequences discussed), and IV. the metabolism of HNE leading to a great number of degradation products, some of which are excreted in urine and may serve as non-invasive biomarkers of oxidative stress.

Role of 4-hydroxynonenal-protein adducts in human diseases

SIGNIFICANCE

Oxidative stress provokes the peroxidation of polyunsaturated fatty acids in cellular membranes, leading to the formation of aldheydes that, due to their high chemical reactivity, are considered to act as second messengers of oxidative stress. Among the aldehydes formed during lipid peroxidation (LPO), 4-hydroxy-2-nonenal (HNE) is produced at a high level and easily reacts with both low-molecular-weight compounds and macromolecules, such as proteins and DNA. In particular, HNE-protein adducts have been extensively investigated in diseases characterized by the pathogenic contribution of oxidative stress, such as cancer, neurodegenerative, chronic inflammatory, and autoimmune diseases.

RECENT ADVANCES

In this review, we describe and discuss recent insights regarding the role played by covalent adducts of HNE with proteins in the development and evolution of those among the earlier mentioned disease conditions in which the functional consequences of their formation have been characterized.

CRITICAL ISSUES

Results obtained in recent years have shown that the generation of HNE-protein adducts can play important pathogenic roles in several diseases. However, in some cases, the generation of HNE-protein adducts can represent a contrast to the progression of disease or can promote adaptive cell responses, demonstrating that HNE is not only a toxic product of LPO but also a regulatory molecule that is involved in several biochemical pathways.

FUTURE DIRECTIONS

In the next few years, the refinement of proteomical techniques, allowing the individuation of novel cellular targets of HNE, will lead to a better understanding the role of HNE in human diseases.

Generation of Adducts of 4-Hydroxy-2-nonenal with Heat Shock 60 kDa Protein 1 in Human Promyelocytic HL-60 and Monocytic THP-1 Cell Lines

Heat shock 60 kDa protein 1 (HSP60) is a chaperone and stress response protein responsible for protein folding and delivery of endogenous peptides to antigen-presenting cells and also a target of autoimmunity implicated in the pathogenesis of atherosclerosis. By two-dimensional electrophoresis and mass spectrometry, we found that exposure of human promyelocytic HL-60 cells to a nontoxic concentration (10 μM) of 4-hydroxy-2-nonenal (HNE) yielded a HSP60 modified with HNE. We also detected adducts of HNE with putative uncharacterized protein CXorf49, the product of an open reading frame identified in various cell and tissue proteomes. Moreover, exposure of human monocytic THP-1 cells differentiated with phorbol 12-myristate 13-acetate to 10 μM HNE, and to light density lipoprotein modified with HNE (HNE-LDL) or by copper-catalyzed oxidation (oxLDL), but not to native LDL, stimulated the formation of HNE adducts with HSP60, as detected by immunoprecipitation and western blot, well over basal levels. The identification of HNE-HSP60 adducts outlines a framework of mutually reinforcing interactions between endothelial cell stressors, like oxLDL and HSP60, whose possible outcomes, such as the amplification of endothelial dysfunction, the spreading of lipoxidative damage to other proteins, such as CXorf49, the activation of antigen-presenting cells, and the breaking of tolerance to HSP60 are discussed.

4-Hydroxynonenal in the pathogenesis and progression of human diseases

Metastable aldehydes produced by lipid peroxidation act as 'toxic second messengers' that extend the injurious potential of free radicals. 4-hydroxy 2-nonenal (HNE), a highly toxic and most abundant stable end product of lipid peroxidation, has been implicated in the tissue damage, dysfunction, injury associated with aging and other pathological states such as cancer, Alzheimer, diabetes, cardiovascular and inflammatory complications. Further, HNE has been considered as a oxidative stress marker and it act as a secondary signaling molecule to regulates a number of cell signaling pathways. Biological activity of HNE depends on its intracellular concentration, which can differentially modulate cell death, growth and differentiation. Therefore, the mechanisms responsible for maintaining the intracellular levels of HNE are most important, not only in the defense against oxidative stress but also in the pathophysiology of a number of disease processes. In this review, we discussed the significance of HNE in mediating various disease processes and how regulation of its metabolism could be therapeutically effective.

Interaction of aldehydes derived from lipid peroxidation and membrane proteins

A great variety of compounds are formed during lipid peroxidation of polyunsaturated fatty acids of membrane phospholipids. Among them, bioactive aldehydes, such as 4-hydroxyalkenals, malondialdehyde (MDA) and acrolein, have received particular attention since they have been considered as toxic messengers that can propagate and amplify oxidative injury. In the 4-hydroxyalkenal class, 4-hydroxy-2-nonenal (HNE) is the most intensively studied aldehyde, in relation not only to its toxic function, but also to its physiological role. Indeed, HNE can be found at low concentrations in human tissues and plasma and participates in the control of biological processes, such as signal transduction, cell proliferation, and differentiation. Moreover, at low doses, HNE exerts an anti-cancer effect, by inhibiting cell proliferation, angiogenesis, cell adhesion and by inducing differentiation and/or apoptosis in various tumor cell lines. It is very likely that a substantial fraction of the effects observed in cellular responses, induced by HNE and related aldehydes, be mediated by their interaction with proteins, resulting in the formation of covalent adducts or in the modulation of their expression and/or activity. In this review we focus on membrane proteins affected by lipid peroxidation-derived aldehydes, under physiological and pathological conditions.

CD36 mediates endothelial dysfunction downstream of circulating factors induced by O3 exposure

Inhaled pollutants induce the release of vasoactive factors into the systemic circulation, but little information is available regarding the nature of these factors or their receptors. The pattern recognition receptor CD36 interacts with many damage-related circulating molecules, leading to activation of endothelial cells and promoting vascular inflammation; therefore, we hypothesized that CD36 plays a pivotal role in mediating cross talk between inhaled ozone (O3)-induced circulating factors and systemic vascular dysfunction. O3 exposure (1 ppm × 4h) induced lung inflammation in wild-type (WT) mice, which was absent in the CD36 deficient (CD36(-/-)) mice. Acetylcholine (ACh)-evoked vasorelaxation was impaired in isolated aortas from O3-exposed WT mice but not in vessels from CD36(-/-) mice. To delineate whether vascular impairments were caused by lung inflammation or CD36-mediated generation of circulating factors, naïve aortas were treated with diluted serum from control or O3-exposed WT mice, which recapitulated the impairments of vasorelaxation observed after inhalation exposures. Aortas from CD36(-/-) mice were insensitive to the effects of O3-induced circulating factors, with robust vasorelaxation responses in the presence of serum from O3-exposed WT mice. Lung inflammation was not a requirement for production of circulating vasoactive factors, as serum from O3-exposed CD36(-/-) mice could inhibit vasorelaxation in naïve WT aortas. These results suggest that O3 inhalation induces the release of circulating bioactive factors capable of impairing vasorelaxation to ACh via a CD36-dependent signaling mechanism. Although lung inflammatory and systemic vascular effects were both dependent on CD36, the presence of circulating factors appears to be independent of CD36 and inflammatory responses.

LOX-1 ligands containing apolipoprotein B and carotid intima-media thickness in middle-aged community-dwelling US Caucasian and Japanese men

OBJECTIVE

The serum level of LOX-1 ligand containing ApoB (LAB) may reflect atherogenicity better than LDL cholesterol (LDLC), total LDL particles and usual measurement of oxidized LDL. The association between LAB and intima-media thickness (IMT) of carotid artery was investigated by ultrasound in US and Japan men.

METHODS

Participants were 297 US Caucasian and 310 Japanese men, aged 40-49 years without past history of cardiovascular disease. Serum LAB levels were measured by ELISAs with recombinant LOX-1 and monoclonal anti-apolipoprotein B antibody.

RESULTS

Serum LAB levels [median (interquartile range), μg/L] were 1321 (936, 1730) in US Caucasians and 940 (688, 1259) in Japanese. For Caucasian men, average IMT was higher in higher LAB quartile, which was 0.653, 0.667, 0.688, and 0.702 mm, respectively (p for trend = 0.02). Linear regression analysis showed serum LAB was significantly associated with IMT after adjustment for LDLC or total LDL particles in addition to other traditional or novel risk factors for atherosclerosis such as C-reactive protein. However, there was no significant relationship between LAB and IMT in Japanese men.

CONCLUSION

Serum LAB, a new candidate biomarker for residual risk, was associated with an increased carotid IMT in US Caucasian men independently of various risk factors; however, ethnic difference should be clarified in the future.

Redox-derived damage-associated molecular patterns: Ligand function of lipid peroxidation adducts

Endogenous electrophiles, such as α,β-unsaturated aldehydes and ketones generated during lipid peroxidation, exhibit a facile reactivity with proteins, generating a variety of intra and intermolecular covalent adducts. It has been postulated that these host-derived, modified proteins with electrophiles, which constitute the products of diverse classes of oxidative reactions, represent damage-associated molecular patterns (DAMPs). The DAMPs, that occur in vivo, can be a ligand of multiple proteins, which in turn, may lead to the profound innate and adaptive immune responses and mediate homeostatic functions consequent to inflammation and cell death.

LOX-1: a multiligand receptor at the crossroads of response to danger signals

PURPOSE OF REVIEW

LOX-1 is a multiligand receptor implicated in endothelial dysfunction and atherosclerosis, although it was originally identified as an oxidized LDL receptor. In this review, the roles of various LOX-1 ligands and their interaction with LOX-1 are discussed to understand the pathophysiological significance of LOX-1.

RECENT FINDINGS

LOX-1 knockout mice showed resistance of endothelium-dependent vasorelaxation against oxidized LDL and retardation of atherosclerosis progression. LOX-1 ligand reduction in mice also attenuated atherosclerosis progression. In a human cohort study, high concentration of apoB-containing LOX-1 ligands predicted the incidence of cardiovascular disease. Furthermore, modified HDL, which existed in high concentration in the plasma of coronary artery disease patients, was found to induce impairment of endothelial nitric oxide release via LOX-1. In addition to lipoproteins, LOX-1 was found to work as a C-reactive protein receptor providing a scaffold for the activation of the complement system.

SUMMARY

LOX-1 is a unique molecule among the sensors of danger signals. LOX-1 is not only sensing danger signals such as modified LDL and heat shock protein, but also scaffolding other danger sensors including C-reactive protein and C1q, and directly commanding responses to danger signals by working as a cell adhesion molecule. Via these functions, LOX-1 might work as a surveillance molecule of vascular homeostasis.