The clinical potential of thiol redox proteomics.

Introduction: Protein thiols are susceptible to oxidation in health and disease. Redox proteomics methods facilitate the identification, quantification, and rationalization of oxidation processes including those involving protein thiols. These residues are crucial to understanding redox homeostasis underpinning normal cell functioning and regulation as well as novel biomarkers of pathology and promising novel drug targets.Areas covered: This article reviews redox proteomic approaches to study of protein thiols in some important human pathologies and assesses the clinical potential of individual Cys residues as novel biomarkers for disease detection and as targets for novel treatments.Expert commentary: Although protein thiols are not as routinely used as redox biomarkers as some other lesions such as carbonylation, there has been growing recent interest in their potential. Driven largely by developments in high-resolution mass spectrometry it is possible now to identify proteins that are redox modified at thiol groups or that interact with regulatory oxidoreductases. Thiols that are specifically susceptible to modification by reactive oxygen species can be routinely identified now and quantitative MS can be used to quantify the proportion of a protein that is redox modified.

The Antiglycoxidative Ability of Selected Phenolic Compounds-An In Vitro Study.

Hyperglycemia and oxidative stress may be observed in different diseases as important factors connected with their development. They often occur simultaneously and are considered together as one process: Glycoxidation. This can influence the function or structure of many macromolecules, for example albumin, by changing their physiological properties. This disturbs the homeostasis of the organism, so the search for natural compounds able to inhibit the glycoxidation process is a current and important issue. The aim of this study was the examination of the antiglycoxidative capacity of 16 selected phenolic compounds, belonging to three phenolic groups, as potential therapeutic agents. Their antiglycoxidative ability, in two concentrations (2 and 20 µM), were examined by in vitro study. The inhibition of the formation of both glycoxidative products (advanced glycation end products (AGEs) and advanced oxidation protein products (AOPPs)) were assayed. Stronger antiglycoxidative action toward the formation of both AOPPs and AGEs was observed for homoprotocatechuic and ferulic acids in lower concentrations, as well as catechin, quercetin, and 8-O-methylurolithin A in higher concentrations. Homoprotocatechuic acid demonstrated the highest antiglycoxidative capacity in both examined concentrations and amongst all of them. A strong, significant correlation between the percentage of AOPPs and AGEs inhibition by compounds from all phenolic groups, in both examined concentrations, was observed. The obtained results give an insight into the antiglycoxidative potential of phenolic compounds and indicate homoprotocatechuic acid to be the most promising antiglycoxidative agent, but further biological and pharmacological studies are needed.

Circulating Advanced Oxidation Protein Products as Oxidative Stress Biomarkers and Progression Mediators in Pathological Conditions Related to Inflammation and Immune Dysregulation.

Evidence came out showing that oxidative stress has a pivotal role in development and maintenance of inflammation and aberrant immune responses. Biomarkers of oxidative stress may define the proportion of oxidative damage underlying pathological conditions, and also foresee and monitor the possible efficacy of therapeutic strategies designed to control these pathologies. New compounds, which can be used as biomarkers, have been identified, and among them advanced oxidation protein products (AOPPs), formed mainly by chlorinated oxidants resulting from activity of myeloperoxidase. Our paper is aimed to review clinical evidences concerning the valuable potential of AOPPs as biomarkers of oxidative injury in development and progression of diseases and chronic conditions related to inflammatory status and immune dysregulation. These pathologies include metabolic syndrome, obesity, immune-mediated inflammatory diseases, neurodegenerative diseases, and cancer. Due to the heterogeneity of pathologies reported to be characterized by AOPP accumulation, it is evident that AOPPs are not merely a marker of neutrophil activation, but at the same time AOPPs cannot always be disease determinants. The data reported in this review corroborate the opinion that AOPPs can be successfully used to in vitro confirm the diagnosis of inflammatory and immune-mediated diseases, but at the same time evidence is that, very likely due to the way through which AOPPs are formed as well as the effect they can contribute to induce, AOPP values cannot be clearly reflective of their involvement in the pathogenesis and in the evolution of a specific disease.

Oxidized plasma albumin promotes platelet-endothelial crosstalk and endothelial tissue factor expression.

Plasma advanced oxidation protein products (AOPPs), a class of pro-inflammatory pathogenic mediators, accumulate in subjects with chronic kidney disease. Whether AOPPs contribute to coagulation abnormalities, which are frequently seen in uremic patients, is unknown. Here we report that AOPPs activate platelets via a CD36-mediated signaling pathway. Activation of signaling pathways by AOPP-platelet interaction resulted in the expression of several platelet activation markers and rapidly induced the expression of CD40 ligand, triggering platelet adhesion to endothelial cells and promoting endothelial tissue factor expression. AOPPs and serum tissue factor levels were considerably increased in end stage renal disease patients on hemodialysis and a significant correlation of AOPPs and serum tissue factor was found. Interestingly, serum levels of AOPPs and tissue factor were substantially lower in stable kidney transplant patients when compared with hemodialysis patients. Given that CD36 is known to transduce the effects of oxidized lipids into platelet hyperactivity, our findings reveal previously unknown pro-thrombotic activities of oxidized plasma albumin via a CD36 dependent pathway.

Mass spectrometry-based methods for identifying oxidized proteins in disease: advances and challenges.

Many inflammatory diseases have an oxidative aetiology, which leads to oxidative damage to biomolecules, including proteins. It is now increasingly recognized that oxidative post-translational modifications (oxPTMs) of proteins affect cell signalling and behaviour, and can contribute to pathology. Moreover, oxidized proteins have potential as biomarkers for inflammatory diseases. Although many assays for generic protein oxidation and breakdown products of protein oxidation are available, only advanced tandem mass spectrometry approaches have the power to localize specific oxPTMs in identified proteins. While much work has been carried out using untargeted or discovery mass spectrometry approaches, identification of oxPTMs in disease has benefitted from the development of sophisticated targeted or semi-targeted scanning routines, combined with chemical labeling and enrichment approaches. Nevertheless, many potential pitfalls exist which can result in incorrect identifications. This review explains the limitations, advantages and challenges of all of these approaches to detecting oxidatively modified proteins, and provides an update on recent literature in which they have been used to detect and quantify protein oxidation in disease.

Kinetics of glycoxidation of bovine serum albumin by glucose, fructose and ribose and its prevention by food components.

The aim of this study was to compare the kinetics of the glycoxidation of bovine serum albumin (BSA) as a model protein by three sugars: glucose, fructose and ribose, using fluorometric measurements of the content of advanced glycation end products (AGEs), protein-bound fructosamine, dityrosine, N'-formylkynurenine, kynurenine, tryptophan, the content of advanced oxidation protein products (AOPP), protein carbonyl groups, as well as thiol groups. Moreover, the levels of glycoalbumin and AGEs were determined by using an enzyme-linked immunosorbent assay. Based on the kinetic results, the optimal incubation time for studies of the modification of the glycoxidation rate by additives was chosen, and the effects of 25 compounds of natural origin on the glycoxidation of BSA induced by various sugars were examined. The same compounds were found to have different effects on glycoxidation induced by various sugars, which suggests caution in extrapolation from experiments based on one sugar to other sugars. From among the compounds tested, the most effective inhibitors of glycoxidation were: polyphenols, pyridoxine and 1-cyano-4-hydroxycinnamic acid.

Advanced oxidation protein products induce cardiomyocyte death via Nox2/Rac1/superoxide-dependent TRAF3IP2/JNK signaling.

Advanced oxidation protein products (AOPPs) are formed during chronic oxidative stress as a result of reactions between plasma proteins and chlorinated oxidants. Their levels are elevated during various cardiovascular diseases. Because elevated AOPPs serve as independent risk factors for ischemic heart disease, and cardiomyocyte death is a hallmark of ischemic heart disease, we hypothesized that AOPPs will induce cardiomyocyte death. AOPP-modified mouse serum albumin (AOPP-MSA) induced significant death of neonatal mouse cardiomyocytes that was attenuated by knockdown of the receptor for advanced glycation end products, but not CD36. Notably, TRAF3-interacting protein 2 (TRAF3IP2; also known as CIKS or Act1) knockdown blunted AOPP-induced apoptosis. AOPP-MSA stimulated Nox2/Rac1-dependent superoxide generation, TRAF3IP2 expression, and TRAF3IP2-dependent JNK activation. The superoxide anion generating xanthine/xanthine oxidase system and hydrogen peroxide both induced TRAF3IP2 expression. Further, AOPP-MSA induced mitochondrial Bax translocation and release of cytochrome c into cytoplasm. Moreover, AOPP-MSA suppressed antiapoptotic Bcl-2 and Bcl-xL expression. These effects were reversed by TRAF3IP2 knockdown or forced expression of mutant JNK. Similar to its effects in neonatal cardiomyocytes, AOPP-MSA induced adult cardiomyocyte death in part via TRAF3IP2. These results demonstrate for the first time that AOPPs induce cardiomyocyte death via Nox2/Rac1/superoxide-dependent TRAF3IP2/JNK activation in vitro and suggest that AOPPs may contribute to myocardial injury in vivo. Thus TRAF3IP2 may represent a potential therapeutic target in ischemic heart disease.

The inhibitory effect of Prunella vulgaris L. on aldose reductase and protein glycation.

To evaluate the aldose reductase (AR) enzyme inhibitory ability of Prunella vulgaris L. extract, six compounds were isolated and tested for their effects. The components were subjected to in vitro bioassays to investigate their inhibitory assays using rat lens aldose reductase (rAR) and human recombinant AR (rhAR). Among them, caffeic acid ethylene ester showed the potent inhibition, with the IC(50) values of rAR and rhAR at 3.2 ± 0.55 µM and 12.58 ± 0.32 µM, respectively. In the kinetic analyses using Lineweaver-Burk plots of 1/velocity and 1/concentration of substrate, this compound showed noncompetitive inhibition against rhAR. Furthermore, it inhibited galactitol formation in a rat lens incubated with a high concentration of galactose. Also it has antioxidative as well as advanced glycation end products (AGEs) inhibitory effects. As a result, this compound could be offered as a leading compound for further study as a new natural products drug for diabetic complications.