4-Hydroperoxy-2-nonenal is not just an intermediate but a reactive molecule that covalently modifies proteins to generate unique intramolecular oxidation products.
ABSTRACT α,β-Unsaturated aldehydes generated during lipid peroxidation, such as 4-oxoalkenals and 4-hydroxyalkenals, can give rise to protein degeneration in a variety of pathological states. Although the covalent modification of proteins by these end products has been well studied, the reactivity of unstable intermediates possessing a hydroperoxy group, such as 4-hydroperoxy-2-nonenal (HPNE), with protein has received little attention. We have now established a unique protein modification in which the 4-hydroperoxy group of HPNE is involved in the formation of structurally unusual lysine adducts. In addition, we showed that one of the HPNE-specific lysine adducts constitutes the epitope of a monoclonal antibody raised against the HPNE-modified protein. Upon incubation with bovine serum albumin, HPNE preferentially reacted with the lysine residues. By employing N(α)-benzoylglycyl-lysine, we detected two major products containing one HPNE molecule per peptide. Based on the chemical and spectroscopic evidence, the products were identified to be the N(α)-benzoylglycyl derivatives of N(ε)-4-hydroxynonanoic acid-lysine and N(ε)-4-hydroxy-(2Z)-nonenoyllysine, both of which are suggested to be formed through mechanisms in which the initial HPNE-lysine adducts undergo Baeyer-Villiger-like reactions proceeding through an intramolecular oxidation catalyzed by the hydroperoxy group. On the other hand, using an HPNE-modified protein as the immunogen, we raised a monoclonal antibody against the HPNE-modified protein and identified one of the HPNE-specific lysine adducts, N(ε)-4-hydroxynonanoic acid-lysine, as an intrinsic epitope of the monoclonal antibody. Furthermore, we demonstrated that the HPNE-specific epitopes were produced not only in the oxidized low density lipoprotein in vitro but also in the atherosclerotic lesions. These results indicated that HPNE is not just an intermediate but also a reactive molecule that could covalently modify proteins in biological systems.
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ABSTRACT: Austin J Pharmacol Ther. 2014; 2 (9).4 Austin J Pharmacol Ther -Volume 2 Issue 9 -2014 Submit your Manuscript | www.austinpublishinggroup.com Anderson et al. © All rights are reserved Austin Journal of Pharmacology and Therapeutics Open Access Full Text Article maladaptation occurs gradually as muscle fibers are encased in extracellular matrix, leading to ventricular wall stiffening and ultimately decompensation which manifests as diastolic dysfunction . Over-production of extracellular matrix has physical effects on the microstructure as well as changes in physiological environment through the release of factors such as transforming growth factor-β(TGF-β) . The most notable change in cellular physiology is the transformation of fibroblasts to myofibroblasts. Myofibroblasts are crucial in the normal response to injury and there is evidence to suggest the processes that trigger this transformation are tissue dependent [28,29]. Myofibroblasts are highly specialized for the secretion of extracellular matrix. Furthermore, they are more responsive to stimulation by factors such cytokines . In certain patients this transition in phenotype to a myofibroblast-predominant population of cells may increase risk of adverse cardiac events [31-33]. For example, since fibrotic tissue lacks electrical conductivity it has been proposed that this change in phenotype may directly account for increased risk of ventricular arrhythmias. Studies show that hyperglycemia/ insulin resistance promotes fibroblast -myofibroblasts transformation . Furthermore in the context of lipid peroxidation it is intriguing that in vitro treatment of human fibroblasts with carbonyl modified proteins produces a similar phenotype transition . This effect may be mitigated by carbonyl scavengers such as carnosine (Box 1) and it is postulated that inhibition of the TGF-β pathway may serve as a potential mechanism . These observations are not confined to patients with metabolic syndrome, in fact in a subset of 'healthy' obese patients with a relatively normal cardiometabolic profile (normotensive, euglycemic), the early stages of irreversible fibrotic cardiac remodeling have been observed . Advanced Glycation End-products, a unique type of carbonyl stress with therapeutic potential The receptor for advanced glycation end-products (RAGE) is a 35KDa receptor that belongs to the immunoglobulin G family of receptors [36,37]. RAGE does not recognize a primary amino acid sequence nor arrangement. It is essentially a pattern recognition receptor (PRR) that displays affinity to a wide variety of glycated proteins . Since in many cases lipid peroxidation end-products (LPPs) and Advanced Glycation End Products (AGE) often share structural homology, proteins modified with LPPs (e.g., HNE, MDA) may serve as candidate ligands for RAGE. The importance of RAGE in diabetic pathologies (retinopathy, neuropathy) is an established and active area of study. In the context of carbonyl stress, RAGE may serve as a key mediator of carbonyl stress in cardiometabolic disease. Formation of AGE occurs through the Maillard reaction. PUFA-derived aldehydes contribute in the conversion of the unstable Schiff Base intermediate in an irreversible rearrangement reaction to a stable Amadori product [39-41]. Therefore in conditions of elevated carbonyl stress, it is plausible that increased cross-linking of Amadori products would shift the dynamic equilibrium even more in favor of EditorialAustin Journal of Pharmacology & Therapeutics. 09/2014; 2(9):4.
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ABSTRACT: Natural antibodies (Abs), predominantly IgMs, play an important function in the host response to the recognition of endogenous danger signals called damage-associated molecular patterns (DAMPs). Many of the natural IgM Abs also show several different antigenic cross-reactivities toward covalently modified proteins, such as oxidized low-density lipoproteins and advanced glycation end products. Of interest, a recent study has shown that these DAMPs have several physicochemical characteristics that differ from native proteins, such as an increased negative charge due to modification of the lysine residues. This finding may provide a mechanistic insight into the multi-specificity of the natural Abs.Free Radical Biology and Medicine 03/2014; · 5.27 Impact Factor
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ABSTRACT: Peroxidation of membranes and lipoproteins converts "inert" phospholipids into a plethora of oxidatively modified phospholipids (oxPL) that can act as signaling molecules. In this review, we will discuss four major classes of oxPL: mildly oxygenated phospholipids, phospholipids with oxidatively truncated acyl chains, phospholipids with cyclized acyl chains, and phospholipids that have been oxidatively N-modified on their headgroups by reactive lipid species. For each class of oxPL we will review the chemical mechanisms of their formation, the evidence for their formation in biological samples, the biological activities and signaling pathways associated with them, and the catabolic pathways for their elimination. We will end by briefly highlighting some of the critical questions that remain about the role of oxPL in physiology and disease.Chemistry and Physics of Lipids 04/2014; · 2.59 Impact Factor