Türk Biyokimya Dergisi [Turkish Journal of Biochemistry – Turk J Biochem] 2006; 31 (2); 51–56.

Diabetes mellitus hastalığının erken ve geç dönem komplikasyonlarının (mikroanjiyopati, nöropati gibi) patogenezinde oksidatif stres önemli bir rol oynamaktadır. Protein glikasyonu ve glikoz oto-oksidasyonu, lipid peroksidasyonuna neden olabilen serbest radikalleri oluşturmaktadır. Oksidatif stresin diğer potansiyel mekanizmaları arasınd a antioksidan savunma sistemlerinin yetersizliği bulunmaktadır. Bu yazıda serbest radikaller ve antioksidan sistem tartışıldı.

Gıda Mühendisliği Dergisi

Dokularda meydana gelen reaktif oksijen türleri (ROS) ve serbest radikaller DNA, protein, karbonhidrat ve lipidler gibi biyolojik açıdan önemli materyallere zarar verebilmektedir. Serbest radikaller vücut dışından gelebileceği gibi insan metabolizmasının doğal bir sonucu olarak da oluşabilmektedir. Serbest radikallerin endojen olarak üretimi farklı yollarla gerçekleşmektedir. Buna karşılık, canlı organizmalar serbest radikallerin potansiyel yıkıcı etkilerine karşı kendilerini korumak için çeşitli mekanizmalara sahiptir. Bu makale, reaktif oksijen türlerinin oluşum mekanizmalarını ve vücuttaki antioksidan savunma sistemlerini kapsamaktadır.

Toxicology Volume 283, Issues 2-3, 10 May 2011, Pages 65-87

Abstract
Detailed studies in the past two decades have shown that redox active metals like iron (Fe), copper (Cu), chromium (Cr), cobalt (Co) and other metals undergo redox cycling reactions and possess the ability to produce reactive radicals such as superoxide anion radical and nitric oxide in biological systems. Disruption of metal ion homeostasis may lead to oxidative stress, a state where increased formation of reactive oxygen species (ROS) overwhelms body antioxidant protection and subsequently induces DNA damage, lipid peroxidation, protein modification and other effects, all symptomatic for numerous diseases, involving cancer, cardiovascular disease, diabetes, atherosclerosis, neurological disorders (Alzheimer’s disease, Parkinson’s disease), chronic inflammation and others. The underlying mechanism of action for all these metals involves formation of the superoxide radical, hydroxyl radical (mainly via Fenton reaction) and other ROS, finally producing mutagenic and carcinogenic malondialdehyde (MDA), 4-hydroxynonenal (HNE) and other exocyclic DNA adducts. On the other hand, the redox inactive metals, such as cadmium (Cd), arsenic (As) and lead (Pb) show their toxic effects via bonding to sulphydryl groups of proteins and depletion of glutathione. Interestingly, for arsenic an alternative mechanism of action based on the formation of hydrogen peroxide under physiological conditions has been proposed. A special position among metals is occupied by the redox inert metal zinc (Zn). Zn is an essential component of numerous proteins involved in the defense against oxidative stress. It has been shown, that depletion of Zn may enhance DNA damage via impairments of DNA repair mechanisms. In addition, Zn has an impact on the immune system and possesses neuroprotective properties. The mechanism of metal-induced formation of free radicals is tightly influenced by the action of cellular antioxidants. Many low-molecular weight antioxidants (ascorbic acid (vitamin C), alpha-tocopherol (vitamin E), glutathione (GSH), carotenoids, flavonoids, and other antioxidants) are capable of chelating metal ions reducing thus their catalytic acitivity to form ROS. A novel therapeutic approach to supress oxidative stress is based on the development of dual function antioxidants comprising not only chelating, but also scavenging components. Parodoxically, two major antioxidant enzymes, superoxide dismutase (SOD) and catalase contain as an integral part of their active sites metal ions to battle against toxic effects of metal-induced free radicals. The aim of this review is to provide an overview of redox and non-redox metal-induced formation of free radicals and the role of oxidative stress in toxic action of metals.

Free Radical Biology & Medicine, Vol. 31, No. 11, pp. 1287–1312, 2001

Abstract
Reactive oxygen species (ROS) are known mediators of intracellular signaling cascades. Excessive production of ROS may, however, lead to oxidative stress, loss of cell function, and ultimately apoptosis or necrosis. A balance between oxidant and antioxidant intracellular systems is hence vital for cell function, regulation, and adaptation to diverse growth conditions. Thioredoxin reductase (TrxR) in conjunction with thioredoxin (Trx) is a ubiquitous oxidoreductase system with antioxidant and redox regulatory roles. In mammals, extracellular forms of Trx also have cytokine-like effects. Mammalian TrxR has a highly reactive active site selenocysteine residue resulting in a profound reductive capacity, reducing several substrates in addition to Trx. Due to the reactivity of TrxR, the enzyme is inhibited by many clinically used electrophilic compounds including nitrosoureas, aurothioglucose, platinum compounds, and retinoic acid derivatives. The properties of TrxR in combination with the functions of Trx position this system at the core of cellular thiol redox control and antioxidant defense. In this review, we focus on the reactions of the Trx system with ROS molecules and different cellular antioxidant enzymes. We summarize the TrxR-catalyzed regeneration of several antioxidant compounds, including ascorbic acid (vitamin C), selenium-containing substances, lipoic acid, and ubiquinone (Q10). We also discuss the general cellular effects of TrxR inhibition. Dinitrohalobenzenes constitute a unique class of immunostimulatory TrxR inhibitors and we consider the immunomodulatory effects of dinitrohalobenzene compounds in view of their reactions with the Trx system.

Keywords: Thioredoxin; Thioredoxin reductase; Redox regulation; Inflammation; Oxidative stress; Antioxidant; Dinitrohalobenzene; Reactive oxygen species; Free radicals

Am J Physiol Cell Physiol. 2008 October; 295(4): C849–C868.

Free radical-induced macromolecular damage has been studied extensively as a mechanism of oxidative stress, but large-scale intervention trials with free radical scavenging antioxidant supplements show little benefit in humans. The present review summarizes data supporting a complementary hypothesis for oxidative stress in disease that can occur without free radicals. This hypothesis, which is termed the “redox hypothesis,” is that oxidative stress occurs as a consequence of disruption of thiol redox circuits, which normally function in cell signaling and physiological regulation. The redox states of thiol systems are sensitive to two-electron oxidants and controlled by the thioredoxins (Trx), glutathione (GSH), and cysteine (Cys). Trx and GSH systems are maintained under stable, but nonequilibrium conditions, due to a continuous oxidation of cell thiols at a rate of about 0.5% of the total thiol pool per minute. Redox-sensitive thiols are critical for signal transduction (e.g., H-Ras, PTP-1B), transcription factor binding to DNA (e.g., Nrf-2, nuclear factor-κB), receptor activation (e.g., αIIbβ3 integrin in platelet activation), and other processes. Nonradical oxidants, including peroxides, aldehydes, quinones, and epoxides, are generated enzymatically from both endogenous and exogenous precursors and do not require free radicals as intermediates to oxidize or modify these thiols. Because of the nonequilibrium conditions in the thiol pathways, aberrant generation of nonradical oxidants at rates comparable to normal oxidation may be sufficient to disrupt function. Considerable opportunity exists to elucidate specific thiol control pathways and develop interventional strategies to restore normal redox control and protect against oxidative stress in aging and age-related disease.
Keywords: thioredoxin, glutathione, cysteine, hydrogen peroxide, redox signaling, protein thiol

Glutathionine (GSH) redox network. A partial list of GSH-dependent proteins illustrates the need for research to understand the integrated function of these redox systems. 1) GSH is synthesized by a two-step pathway in which abundance of two enzymes, glutamate cysteine ligase (GSH0, GSH1) and GSH synthetase (GSHB), determine synthesis rate (97). GSH is degraded by γ-glutamyltransferase (GGT) at the surface of the brush border of the kidney, small intestine, and a number of other tissues, and probably also in the cisternae of the secretory pathway (142). 2) GSH is transported out of cells by several multidrug resistance proteins (MRP) (12). The chloride channel, which is mutated in cystic fibrosis (CFTR), also transports GSH (113), and GSH is transported into mitochondria by the dicarboxylate carrier (DIC) and a monocarboxylate carrier (OGCP) (103). GSH is transported into the cisternae of the endoplasmic reticulum (13), but the molecular nature of the transporter is not known. 3) GSH is used by a number of GSH transferases (GST), which include microsomal and nonmicrosomal locations, to modify electrophilic chemicals (9). These are thought to largely function in detoxification, but some also act on biosynthetic intermediates for prostaglandins and leukotrienes. A fraction of GSH is present as S-nitroso-GSH, a transnitrosylating agent generated from nitric oxide or its metabolites (168). 4) GSH functions in metabolism as a coenzyme for formaldehyde dehydrogenase, glyoxylase, and other metabolic reactions (4, 168). In these reactions, GSH is cyclically removed by one reaction and regenerated in a second reaction. 5) Several thiol transferases, also known as glutaredoxins, catalyze introduction and removal of GSH (110, 114). 5a) Several proteins are regulated by GS-ylation, and many others undergo GS-ylation under oxidative stress conditions (44, 93). 6) GSH is used as a reductant for selenium-dependent GSH peroxidases (GPX) and selenium-independent peroxiredoxin-6 (PRX6) and some GSH transferases (GST). 6a) The product of these oxidative reactions, GSSG, is reduced back to GSH by GSSG reductase (GSHR) in most tissues. In sperm, thioredoxin reductase-3 (TRXR3) has activity toward both Trx and GSH. The proteins included in this figure are present in multiple cellular compartments and are differentially expressed in cells so that development of functional maps will require tissue-specific measurements of individual reaction rates. Protein designations and common names are from the UniProtKB/Swiss-Prot database. Abbreviations are as follows: GSH0, Glu-Cys ligase, regulatory; GSH1, Glu-Cys ligase, catalytic; GSHB, GSH synthetase; GGT1,4, 5, 6, γ-glutamyltransferase; DIC, mitochondrial dicarboxylate carrier (SLC25A10); OGCP, mitochondrial 2-oxoglutarate/malate carrier; CFTR, cystic fibrosis transmembrane conductance protein; MRP, multidrug resistance-associated protein; MRP2, canalicular multispecific organic anion transporter 1; GST, GSH transferase; ADHX, alcohol dehydrogenase class-3; ESTD, S-formyl-GSH hydrolase; GLO2, Glyoxalase II; HAGHL, hydroxyacylGSH hydrolase-like; LGUL, lactoylGSH lyase; MAAI , maleylacetoacetate isomerase; PTGD2, GSH-requiring prostaglandin D synthase; PTGDS, prostaglandin-H2 D-isomerase; PTGES, prostaglandin E synthase; RBP1, RalA-binding protein 1 (RalBP1); GLRX, glutaredoxin and glutaredoxin-related proteins; YD286, glutaredoxin-like protein; GPX, GSH peroxidase; GSHR, GSSG reductase; TRXR3, thioredoxin reductase 3.

J Clin Invest. 2005 March 1; 115(3): 500–508.

A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.

Figure 1
Role of oxygen in myocardial metabolism. (A) Schematic depiction of the pathways by which cardiac muscle utilizes various fuels, including fatty acids, glucose, lactate, and ketones. Glycolysis occurs in the cytosol and does not require oxygen. &豪-Oxidation of fatty acids, ketone metabolism, and the metabolism of glucose-derived intermediates all generate reduced flavoproteins (NADH2 and FADH2). (B) Schematic depiction of the process of oxidative phosphorylation in the mitochondria. Complexes 1_4 refer to specific electron transfer steps that occur in the mitochondria. A series of electron transfers among the flavoproteins (FMNH2, NADH2, FADH2), iron-sulfur, coenzyme Q, and the cytochromes a_c1, results in accumulation of protons in the space between the inner and outer mitochondrial membranes. This proton gradient provides the energy for ATP production via complex 5. Sustaining this crucial process requires the continuous availability of oxygen as the terminal electron acceptor in the chain. Fe2+S, reduced iron-sulfur; Fe3+S, oxidized iron-sulfur; FMN, flavin mononucleotide; cyt, cytochrome; CoQ, coenzyme Q.

Figure 2
Mechanisms by which ROS can alter the structure and function of cardiac muscle. ATII binds a G-protein_associated receptor, initiating a cascade of events that involves activation of O2–– production by the NAD(P)H oxidase NOX2. O2–– is converted by SOD into H2O2 and –OH that mediates activation of MAPKs via a tyrosine kinase. MAPK activation can lead to cardiac hypertrophy or to apoptosis. The ROS that is generated can also signal through ASK-1 to induce cardiac hypertrophy, apoptosis, or phosphorylate troponin T, an event that reduces myofilament sensitivity and cardiac contractility. NO production by the NO synthases iNOS and eNOS can interact with O2–– to form ONOO––. ONOO–– can cause lipid peroxidation, an event that can alter ion channel and ion pump function. Catalase and glutathione reductase (GPx) are shown as enzymatic pathways to produce water and oxygen from H2O2.

Diabetes Care February 2008 vol. 31 no. Supplement 2 S185-S189

Hypertension is associated with increased vascular oxidative stress; however, there is still a debate whether oxidative stress is a cause or a result of hypertension. Animal studies have generally supported the hypothesis that increased blood pressure is associated with increased oxidative stress; however, human studies have been inconsistent. Oxidative stress promotes vascular smooth muscle cell proliferation and hypertrophy and collagen deposition, leading to thickening of the vascular media and narrowing of the vascular lumen. In addition, increased oxidative stress may damage the endothelium and impair endothelium-dependent vascular relaxation and increases vascular contractile activity. All these effects on the vasculature may explain how increased oxidative stress can cause hypertension. Treatment with antioxidants has been suggested to lower oxidative stress and therefore blood pressure. However, to date, clinical studies investigating antioxidant supplements have failed to show any consistent benefit. It is noteworthy that lowering blood pressure with antihypertensive medications is associated with reduced oxidative stress. Therefore, it seems that oxygen stress is not the cause, but rather a consequence, of hypertension.

Diabetes Care February 2008 vol. 31 no. Supplement 2 S181-S184

Recently oxidative stress has been proposed as the cause of hypertension. An imbalance in superoxide and nitric oxide production may account for reduced vasodilation, which in turn can favor the development of hypertension. In vitro and in human studies support this hypothesis. The supplementation of antioxidants, particularly in the form of fresh fruit and vegetables, reduces blood pressure, supporting a role for free radicals in hypertension.

Clinica Chimica Acta 390 (2008) 1–11

As the red cell emerges from the bone marrow, it loses its nucleus, ribosomes, and mitochondria and therefore all capacity for protein synthesis. However, because of the high O2 tension in arterial blood and heme Fe content, reactive oxygen species (ROS) are continuously produced within red cells. Erythrocytes transport large amount of oxygen over their lifespan resulting in oxidative stress. Various factors can lead to the generation of oxidizing radicals such as O2•−, H2O2, HO• in erythrocytes. Evidence indicates that many physiological and pathological conditions such as aging, inflammation, eryptosis develop through ROS action. As such, red cells have potent antioxidant protection consisting of enzymatic and nonenzymatic pathways that modify highly ROS into substantially less reactive intermediates.

The object of this review is to shed light on the role of ROS both at physiological and pathological levels and the structural requirements of antioxidants for appreciable radical-scavenging activity. Obviously, much is still to be discovered before we clearly understand mechanisms of free radical systems in erythrocytes. Ongoing trends in the field are recognition of undetermined oxidant/antioxidant interactions and elucidation of important signaling networks in radical metabolism.

Clinical Chemistry. 2006;52:601-623

Oxidative/nitrosative stress, a pervasive condition of increased amounts of reactive oxygen/nitrogen species, is now recognized to be a prominent feature of many acute and chronic diseases and even of the normal aging process. However, definitive evidence for this association has often been lacking because of recognized shortcomings with biomarkers and/or methods available to assess oxidative stress status in humans. Emphasis is now being placed on biomarkers of oxidative stress, which are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to therapeutic intervention. To be a predictor of disease, a biomarker must be validated. Validation criteria include intrinsic qualities such as specificity, sensitivity, degree of inter- and intraindividual variability, and knowledge of the confounding and modifying factors. In addition, characteristics of the sampling and analytical procedures are of relevance, including constraints and noninvasiveness of sampling, stability of potential biomarkers, and the simplicity, sensitivity, specificity, and speed of the analytical method. Here we discuss some of the more commonly used biomarkers of oxidative/nitrosative damage and include selected examples of human studies.

Endocrine Reviews 2002; 23 (5): 599-622

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-B, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-B, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, -lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

I. Introduction

II. Overview of the Development of Type 2 Diabetes

III. Oxidative Stress and Complications of Diabetes
A. Hyperglycemia leads to mitochondrial dysfunction and activation of stress pathways both in vitro and in vivo
B. ROS generation and oxidative stress
C. NF-B: a primary target for activation by hyperglycemia, ROS, oxidative stress, and inflammatory cytokines
D. Hyperglycemia-dependent NF-B activation in patients with diabetes mellitus
E. Decreased levels of antioxidants in diabetes and prevention of NF-B activation by antioxidants
F. VEGF: an initiator of diabetic complications?
G. Antioxidants inhibit VEGF production
H. JNK/SAPK and p38 MAPK pathways: other primary targets for activation by hyperglycemia, ROS, and inflammatory cytokines
I. Additional important hyperglycemia-activated pathways
J. ROS generation by enzymatic pathways of arachidonic/linoleic acid metabolism

IV. Oxidative Stress and Insulin Resistance
A. Activation of stress-kinases, IRS phosphorylation, and insulin resistance
B. IKKß, IRS proteins, and insulin resistance
C. Oxidative stress, protein tyrosine phosphatases, and insulin resistance
D. Obesity, fatty acids, and insulin resistance
E. Fatty acids and insulin resistance
F. Fatty acids, redox balance, and activation of stress pathways

V. Oxidative Stress and ß-Cell Dysfunction
A. ß-Cell glucose-induced toxicity
B. ß-Cell lipid-induced toxicity
C. ß-Cell combined glucose/lipid toxicity
D. Role of oxidative stress in ß-cell dysfunction
VI. Conclusions and Implications