Aldose reductase-catalyzed reduction of aldehyde phospholipids

Carnosine Supplementation Mitigates the Deleterious Effects of Particulate Matter Exposure in Mice

Background Exposure to fine airborne particulate matter ( PM 2.5) induces quantitative and qualitative defects in bone marrow-derived endothelial progenitor cells of mice, and similar outcomes in humans may contribute to vascular dysfunction and the cardiovascular morbidity and mortality associated with PM 2.5 exposure. Nevertheless, mechanisms underlying the pervasive effects of PM 2.5 are unclear and effective interventional strategies to mitigate against PM 2.5 toxicity are lacking. Furthermore, whether PM 2.5 exposure affects other types of bone marrow stem cells leading to additional hematological or immunological dysfunction is not clear. Methods and Results Mice given normal drinking water or that supplemented with carnosine, a naturally occurring, nucleophilic di-peptide that binds reactive aldehydes, were exposed to filtered air or concentrated ambient particles. Mice drinking normal water and exposed to concentrated ambient particles demonstrated a depletion of bone marrow hematopoietic stem cells but no change in mesenchymal stem cells. However, HSC depletion was significantly attenuated when the mice were placed on drinking water containing carnosine. Carnosine supplementation also increased the levels of carnosine-propanal conjugates in the urine of CAPs-exposed mice and prevented the concentrated ambient particles-induced dysfunction of endothelial progenitor cells as assessed by in vitro and in vivo assays. Conclusions These results suggest that exposure to PM 2.5 has pervasive effects on different bone marrow stem cell populations and that PM 2.5-induced hematopoietic stem cells depletion, endothelial progenitor cell dysfunction, and defects in vascular repair can be mitigated by excess carnosine. Carnosine supplementation may be a viable approach for preventing PM 2.5-induced immune dysfunction and cardiovascular injury in humans.

Aldose reductase inhibitors: 2013-present

INTRODUCTION

Aldose reductase (ALR2) is both the key enzyme of the polyol pathway, whose activation under hyperglycemic conditions leads to the development of chronic diabetic complications, and the crucial promoter of inflammatory and cytotoxic conditions, even under a normoglycemic status. Accordingly, it represents an excellent drug target and a huge effort is being done to disclose novel compounds able to inhibit it.

AREAS COVERED

This literature survey summarizes patents and patent applications published over the last 5 years and filed for natural, semi-synthetic and synthetic ALR2 inhibitors. Compounds described have been discussed and analyzed from both chemical and functional angles.

EXPERT OPINION

Several ALR2 inhibitors with a promising pre-clinical ability to address diabetic complications and inflammatory diseases are being developed during the observed timeframe. Natural compounds and plant extracts are the prevalent ones, thus confirming the use of phytopharmaceuticals as an increasingly pursued therapeutic trend also in the ALR2 inhibitors field. Intriguing hints may be taken from synthetic derivatives, the most significant ones being represented by the differential inhibitors ARDIs. Differently from classical ARIs, these compounds should fire up the therapeutic efficacy of the class while minimizing its side effects, thus overcoming the existing limits of this kind of inhibitors.

A comprehensive narrative review of diagnostic biomarkers in human primary membranous nephropathy

Membranous nephropathy (MN) is relatively major cause of nephrotic syndrome in adults which is recognized as an organ-specific autoimmune disease. The etiology of most cases is idiopathic, whereas the secondary MN is caused by systemic autoimmune diseases, infections, medications and malignancies. The idiopathic disease is developed by the formation of sub-epithelial immune complex deposits most likely due to binding the circulating auto-antibodies to intrinsic antigen on podocytes. The major auto antibody is the anti-phospholipase A2 receptor (anti-PLA2R), however, it is not enough sensitive. Several attempts for diagnostic biomarker identification by modern analytical technologies have been devoted recently. This article reviews the biomarker candidates for primary type of MN that are detected by different approaches on human subjects.

Measurement of Reactive Oxygen Species, Reactive Nitrogen Species, and Redox-Dependent Signaling in the Cardiovascular System: A Scientific Statement From the American Heart Association

Reactive oxygen species and reactive nitrogen species are biological molecules that play important roles in cardiovascular physiology and contribute to disease initiation, progression, and severity. Because of their ephemeral nature and rapid reactivity, these species are difficult to measure directly with high accuracy and precision. In this statement, we review current methods for measuring these species and the secondary products they generate and suggest approaches for measuring redox status, oxidative stress, and the production of individual reactive oxygen and nitrogen species. We discuss the strengths and limitations of different methods and the relative specificity and suitability of these methods for measuring the concentrations of reactive oxygen and reactive nitrogen species in cells, tissues, and biological fluids. We provide specific guidelines, through expert opinion, for choosing reliable and reproducible assays for different experimental and clinical situations. These guidelines are intended to help investigators and clinical researchers avoid experimental error and ensure high-quality measurements of these important biological species.

Aldo-keto Reductase 1B15 (AKR1B15): a mitochondrial human aldo-keto reductase with activity toward steroids and 3-keto-acyl-CoA conjugates

Aldo-keto reductases (AKRs) comprise a superfamily of proteins involved in the reduction and oxidation of biogenic and xenobiotic carbonyls. In humans, at least 15 AKR superfamily members have been identified so far. One of these is a newly identified gene locus, AKR1B15, which clusters on chromosome 7 with the other human AKR1B subfamily members (i.e. AKR1B1 and AKR1B10). We show that alternative splicing of the AKR1B15 gene transcript gives rise to two protein isoforms with different N termini: AKR1B15.1 is a 316-amino acid protein with 91% amino acid identity to AKR1B10; AKR1B15.2 has a prolonged N terminus and consists of 344 amino acid residues. The two gene products differ in their expression level, subcellular localization, and activity. In contrast with other AKR enzymes, which are mostly cytosolic, AKR1B15.1 co-localizes with the mitochondria. Kinetic studies show that AKR1B15.1 is predominantly a reductive enzyme that catalyzes the reduction of androgens and estrogens with high positional selectivity (17β-hydroxysteroid dehydrogenase activity) as well as 3-keto-acyl-CoA conjugates and exhibits strong cofactor selectivity toward NADP(H). In accordance with its substrate spectrum, the enzyme is expressed at the highest levels in steroid-sensitive tissues, namely placenta, testis, and adipose tissue. Placental and adipose expression could be reproduced in the BeWo and SGBS cell lines, respectively. In contrast, AKR1B15.2 localizes to the cytosol and displays no enzymatic activity with the substrates tested. Collectively, these results demonstrate the existence of a novel catalytically active AKR, which is associated with mitochondria and expressed mainly in steroid-sensitive tissues.

Oxidative and reductive metabolism of lipid-peroxidation derived carbonyls

Extensive research has shown that increased production of reactive oxygen species (ROS) results in tissue injury under a variety of pathological conditions and chronic degenerative diseases. While ROS are highly reactive and can incite significant injury, polyunsaturated lipids in membranes and lipoproteins are their main targets. ROS-triggered lipid-peroxidation reactions generate a range of reactive carbonyl species (RCS), and these RCS spread and amplify ROS-related injury. Several RCS generated in oxidizing lipids, such as 4-hydroxy trans-2-nonenal (HNE), 4-oxo-2-(E)-nonenal (ONE), acrolein, malondialdehyde (MDA) and phospholipid aldehydes have been shown to be produced under conditions of oxidative stress and contribute to tissue injury and dysfunction by depleting glutathione and other reductants leading to the modification of proteins, lipids, and DNA. To prevent tissue injury, these RCS are metabolized by several oxidoreductases, including members of the aldo-keto reductase (AKR) superfamily, aldehyde dehydrogenases (ALDHs), and alcohol dehydrogenases (ADHs). Metabolism via these enzymes results in RCS inactivation and detoxification, although under some conditions, it can also lead to the generation of signaling molecules that trigger adaptive responses. Metabolic transformation and detoxification of RCS by oxidoreductases prevent indiscriminate ROS toxicity, while at the same time, preserving ROS signaling. A better understanding of RCS metabolism by oxidoreductases could lead to the development of novel therapeutic interventions to decrease oxidative injury in several disease states and to enhance resistance to ROS-induced toxicity.

Synthesis of optically pure (S)-2-amino-5-arylpent-4-ynoic acids by Sonogashira reactions and their potential use as highly selective potent inhibitors of aldose reductase

A new and convenient synthesis of optically pure (S)-2-amino-5-[aryl]pent-4-ynoic acids (alkynylated amino acids) is reported.

Lipid peroxidation generates biologically active phospholipids including oxidatively N-modified phospholipids

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.

Development of aldose reductase inhibitors for the treatment of inflammatory disorders

INTRODUCTION

Accumulating evidence attributes a significant role to aldose reductase (ALR2) in the pathogenesis of several inflammatory pathologies. Aldose reductase inhibitors (ARIs) were found to attenuate reactive oxygen species (ROS) production both in vitro and in vivo. Thus, they disrupt signaling cascades that lead to the production of cytokines/chemokines, which induce and exacerbate inflammation. As a result, ARIs might hold a significant therapeutic potential as alternate anti-inflammatory drugs.

AREAS COVERED

The authors present a comprehensive review of the current data that support the central role of ALR2 in several inflammatory pathologies (i.e., diabetes, cancer, sepsis, asthma and ocular inflammation). Further, the authors describe the potential underlying molecular mechanisms and provide a commentary on the status of ARIs in this field.

EXPERT OPINION

It is important that future efforts focus on delineating all the steps of the molecular mechanism that implicates ALR2 in inflammatory pathologies. At the same time, utilizing the previous efforts in the field of ARIs, several candidates that have been proven safe in the clinic may be evaluated for their clinical significance as anti-inflammatory medication. Finally, structurally novel ARIs, designed to target specifically the proinflammatory subpocket of ALR2, should be pursued.

Hyperglycemia and endothelial dysfunction in atherosclerosis: lessons from type 1 diabetes

A clear relationship between diabetes and cardiovascular disease has been established for decades. Despite this, the mechanisms by which diabetes contributes to plaque formation remain in question. Some of this confusion derives from studies in type 2 diabetics where multiple components of metabolic syndrome show proatherosclerotic effects independent of underlying diabetes. However, the hyperglycemia that defines the diabetic condition independently affects atherogenesis in cell culture systems, animal models, and human patients. Endothelial cell biology plays a central role in atherosclerotic plaque formation regulating vessel permeability, inflammation, and thrombosis. The current paper highlights the mechanisms by which hyperglycemia affects endothelial cell biology to promote plaque formation.

A potential therapeutic role for aldose reductase inhibitors in the treatment of endotoxin-related inflammatory diseases

INTRODUCTION

Aldose reductase (AR) was initially thought to be involved in the secondary diabetic complications because of its glucose-reducing potential. However, evidence from recent studies indicates that AR is an excellent reducer of a number of lipid peroxidation-derived aldehydes as well as their glutathione conjugates, which regulate inflammatory signals initiated by oxidants such as cytokines, growth factors and bacterial endotoxins, and revealed the potential use of AR inhibition as an approach to prevent inflammatory complications.

AREAS COVERED

An extensive Internet and Medline search was performed to retrieve information on understanding the role of AR inhibition in the pathophysiology of endotoxin-mediated inflammatory disorders. Overall, inhibition of AR appears to be a promising strategy for the treatment of endotoxemia, sepsis and other related inflammatory diseases.

EXPERT OPINION

Current knowledge provides enough evidence to indicate that AR inhibition is a logical therapeutic strategy for the treatment of endotoxin-related inflammatory diseases. Since AR inhibitors have already gone to Phase III clinical studies for diabetic complications and found to be safe for human use, their use in endotoxin-related inflammatory diseases could be expedited. However, one of the major challenges will be the discovery of AR-regulated clinically relevant biomarkers to identify susceptible individuals at risk of developing inflammatory diseases, thereby warranting future research in this area.

Hydroxyalkenals and oxidized phospholipids modulation of endothelial cytoskeleton, focal adhesion and adherens junction proteins in regulating endothelial barrier function

Lipid peroxidation of polyunsaturated fatty acids generates bioactive aldehydes, which exhibit pro- and anti-inflammatory effects in cells and tissues. Accumulating evidence indicates that 4-hydroxynonenal (4-HNE), a major aldehyde derived from lipid peroxidation of n-6 polyunsaturated fatty acids trigger signals that modulates focal adhesion and adherens junction proteins thereby inducing endothelial barrier dysfunction. Similarly, oxidized phospholipids (Ox-PLs) generated by lipid peroxidation of phospholipids with polyunsaturated fatty acids have been implicated in atherogenesis, inflammation and gene expression. Interestingly, physiological concentration of Ox-PLs is anti-inflammatory and protect against endotoxin- and ventilator-associated acute lung injury. Thus, excess generation of bioactive hydroxyalkenals and Ox-PLs during oxidative stress contributes to pathophysiology of various diseases by modulating signaling pathways that regulate pro- and anti-inflammatory responses and barrier regulation. This review summarizes the role of 4-HNE and Ox-PLs affecting cell signaling pathways and endothelial barrier dysfunction through modulation of the activities of proteins/enzymes by Michael adducts formation, enhancing the level of protein tyrosine phosphorylation of the target proteins, and by reorganization of cytoskeletal, focal adhesion, and adherens junction proteins. A better understanding of molecular mechanisms of hydroxyalkenals- and Ox-PLs-mediated pro-and anti-inflammatory responses and barrier function may lead to development of novel therapies to ameliorate oxidative stress related cardio-pulmonary disorders.

Reductive metabolism increases the proinflammatory activity of aldehyde phospholipids

The generation of oxidized phospholipids in lipoproteins has been linked to vascular inflammation in atherosclerotic lesions. Products of phospholipid oxidation increase endothelial activation; however, their effects on macrophages are poorly understood, and it is unclear whether these effects are regulated by the biochemical pathways that metabolize oxidized phospholipids. We found that incubation of 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) with THP-1-derived macrophages upregulated the expression of cytokine genes, including granulocyte/macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor (TNF)-α, monocyte chemotactic protein 1 (MCP-1), interleukin (IL)-1β, IL-6, and IL-8. In these cells, reagent POVPC was either hydrolyzed to lyso-phosphatidylcholine (lyso-PC) or reduced to 1-palmitoyl-2-(5-hydroxy-valeroyl)-sn-glycero-3-phosphocholine (PHVPC). Treatment with the phospholipase A(2) (PLA(2)) inhibitor, pefabloc, decreased POVPC hydrolysis and increased PHVPC accumulation. Pefabloc also increased the induction of cytokine genes in POVPC-treated cells. In contrast, PHVPC accumulation and cytokine production were decreased upon treatment with the aldose reductase (AR) inhibitor, tolrestat. In comparison with POVPC, lyso-PC led to 2- to 3-fold greater and PHVPC 10- to 100-fold greater induction of cytokine genes. POVPC-induced cytokine gene induction was prevented in bone-marrow derived macrophages from AR-null mice. These results indicate that although hydrolysis is the major pathway of metabolism, reduction further increases the proinflammatory responses to POVPC. Thus, vascular inflammation in atherosclerotic lesions is likely to be regulated by metabolism of phospholipid aldehydes in macrophages.

Human aldose reductase expression accelerates atherosclerosis in diabetic apolipoprotein E-/- mice

OBJECTIVE

There are several pathways that mediate the aberrant metabolism of glucose and that might induce greater vascular damage in the setting of diabetes. The polyol pathway mediated by aldose reductase (AR) has been postulated to be one such pathway. However, it has been reported that AR reduces toxic lipid aldehydes and, under some circumstances, might be antiatherogenic.

METHODS AND RESULTS

Atherosclerosis development was quantified in 2 lines of transgenic mice expressing human AR (hAR) crossed on the apolipoprotein E knockout background. The transgenes were used to increase the normally low levels of this enzyme in wild-type mice. Both generalized hAR overexpression and hAR expression via the Tie 2 promoter increased lesion size in streptozotocin diabetic mice. In addition, pharmacological inhibition of AR reduced lesion size.

CONCLUSIONS

Although in some settings AR expression might reduce levels of toxic aldehydes, transgenic expression of this enzyme within the artery wall leads to greater atherosclerosis.

Catalytic reduction of carbonyl groups in oxidized PAPC by Kvβ2 (AKR6)

The β-subunits of the voltage-gated potassium channel (Kvβ) belong to the aldo-keto reductase superfamily. The Kvβ-subunits dock with the pore-forming Kv α-subunits and impart or accelerate the rate of inactivation in Kv channels. Inactivation of Kv currents by Kvβ is differentially regulated by oxidized and reduced pyridine nucleotides. In mammals, AKR6 family is comprised of 3 different genes Kvβ1-3. We have shown previously that Kvβ2 catalyzes the reduction of a broad range of carbonyls including aromatic carbonyls, electrophilic aldehydes and prostaglandins. However, the endogenous substrates for Kvβ have not been identified. To determine whether products of lipid oxidation are substrates of Kvβs, we tested the enzymatic activity of Kvβ2 with oxidized phospholipids generated during the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC). Electrospray ionization mass spectrometric analysis showed that Kvβ2 catalyzed the NADPH-dependent reduction of several products of oxPAPC, including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC), 1-palmitoyl-2-(epoxycyclopentenone)-sn-glycero-3-phosphorylcholine (PECPC), 1-palmitoyl-2-(5,6)- epoxyisoprostane E2-sn-glycero-3-phosphocholine (PEIPC). These results were validated using high resolution mass spectrometric analysis. Time course analysis revealed that the reduced products reached significant levels for ions at m/z 594/596 (POVPC/PHVPC), 810/812 (PECPC/2H-PECPC) and 828/830 (PEIPC/2H-PEIPC) in the oxPAPC+Kvβ2 mixture (p<0.01). These results suggest that Kvβ could serve as a sensor of lipid oxidation via its catalytic activity and thereby alter Kv currents under conditions of oxidative stress.

Functional expression of novel human and murine AKR1B genes

The Aldo Keto Reductases (AKRs) are a superfamily of enzymes that catalyze the reduction of biogenic and xenobiotic aldehydes and ketones. AKR1B family has 2 known members in humans and 3 in rodents. Two novel gene loci, hereafter referred to as AKR1B15 in human and Akr1b16 in mouse have been predicted to exist within the AKR1B clusters. AKR1B15 displays 91% and 67% sequence identity with human genes AKR1B10 and AKR1B1, respectively while Akr1b16 shares 82-84% identity with murine Akr1b8 and Akr1b7. We tested the hypothesis that AKR1B15 and Akr1b16 genes are expressed as functional proteins in human and murine tissues, respectively. Using whole tissue mRNA, we were able to clone the full-length open reading frames for AKR1B15 from human eye and testes, and Akr1b16 from murine spleen, demonstrating that these genes are transcriptionally active. The corresponding cDNAs were cloned into pET28a and pIRES-hrGFP-1α vectors for bacterial and mammalian expression, respectively. Both genes were expressed as 36kDa proteins found in the insoluble fraction of bacterial cell lysate. These proteins, expressed in bacteria showed no enzymatic activity. However, lysates from COS-7 cells transfected with AKR1B15 showed a 4.8-fold (with p-nitrobenzaldehyde) and 3.3-fold (with dl-glyceraldehyde) increase in enzyme activity compared with untransfected COS-7 cells. The Akr1b16 transcript was shown to be ubiquitously expressed in murine tissues. Highest levels of transcript were found in heart, spleen, and lung. From these observations we conclude that the predicted AKR1B15 and 1b16 genes are expressed in several murine and human tissues. Further studies are required to elucidate their physiological roles.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Autoimmunity in membranous nephropathy targets aldose reductase and SOD2

Glomerular targets of autoimmunity in human membranous nephropathy are poorly understood. Here, we used a combined proteomic approach to identify specific antibodies against podocyte proteins in both serum and glomeruli of patients with membranous nephropathy (MN). We detected specific anti-aldose reductase (AR) and anti-manganese superoxide dismutase (SOD2) IgG(4) in sera of patients with MN. We also eluted high titers of anti-AR and anti-SOD2 IgG(4) from microdissected glomeruli of three biopsies of MN kidneys but not from biopsies of other glomerulonephritides characterized by IgG deposition (five lupus nephritis and two membranoproliferative glomerulonephritis). We identified both antigens in MN biopsies but not in other renal pathologies or normal kidney. Confocal and immunoelectron microscopy (IEM) showed co-localization of anti-AR and anti-SOD2 with IgG(4) and C5b-9 in electron-dense podocyte immune deposits. Preliminary in vitro experiments showed an increase of SOD2 expression on podocyte plasma membrane after treatment with hydrogen peroxide. In conclusion, our data support AR and SOD2 as renal antigens of human MN and suggest that oxidative stress may drive glomerular SOD2 expression.

Reductive metabolism of AGE precursors: a metabolic route for preventing AGE accumulation in cardiovascular tissue

OBJECTIVE

To examine the role of aldo-keto reductases (AKRs) in the cardiovascular metabolism of the precursors of advanced glycation end products (AGEs).

RESEARCH DESIGN AND METHODS

Steady-state kinetic parameters of AKRs with AGE precursors were determined using recombinant proteins expressed in bacteria. Metabolism of methylglyoxal and AGE accumulation were studied in human umbilical vein endothelial cells (HUVECs) and C57 wild-type, akr1b3 (aldose reductase)-null, cardiospecific-akr1b4 (rat aldose reductase), and akr1b8 (FR-1)-transgenic mice. AGE accumulation and atherosclerotic lesions were studied 12 weeks after streptozotocin treatment of C57, akr1b3-null, and apoE- and akr1b3-apoE-null mice.

RESULTS

Higher levels of AGEs were generated in the cytosol than at the external surface of HUVECs cultured in high glucose, indicating that intracellular metabolism may be an important regulator of AGE accumulation and toxicity. In vitro, AKR 1A and 1B catalyzed the reduction of AGE precursors, whereas AKR1C, AKR6, and AKR7 were relatively ineffective. Highest catalytic efficiency was observed with AKR1B1. Acetol formation in methylglyoxal-treated HUVECs was prevented by the aldose reductase inhibitor sorbinil. Acetol was generated in hearts perfused with methylglyoxal, and its formation was increased in akr1b4- or akr1b8-transgenic mice. Reduction of AGE precursors was diminished in hearts from akr1b3-null mice. Diabetic akr1b3-null mice accumulated more AGEs in the plasma and the heart than wild-type mice, and deletion of akr1b3 increased AGE accumulation and atherosclerotic lesion formation in apoE-null mice.

CONCLUSIONS

Aldose reductase-catalyzed reduction is an important pathway in the endothelial and cardiac metabolism of AGE precursors, and it prevents AGE accumulation and atherosclerotic lesion formation.

Aldose reductase is a potent regulator of TGF-β1 induced expression of fibronectin in human mesangial cells

Glomerulosclerosis is considered to be the final pathway leading to the progressive loss of renal function in several kidney diseases, transforming growth factor β1 (TGF-β1) plays a critical role in glomerulosclerosis. However, the mechanisms of TGF-β1 stimulating glomerulosclerosis remain poorly understood. Here we report that TGF-β1-induced expression of fibronectin (FN) depends on the activity of aldose reductase (AR) in human mesangial cells (HMCs).The results show that TGF-β1 increased the expression of FN, which attenuated by pharmacological inhibition of AR or knockdown of the enzyme by small interfering RNA (siRNA). MAPKs (ERK, JNK and p38) signalling pathways were activated in HMCs after stimulated by TGF-β1, inhibition of AR blunted the activation ERK, p38 and JNK signalling pathways. These changes were associated with decreased TGF-β1-induced expression of FN. These results indicate that AR is a potent regulator of TGF-β1 induced expression of FN in human mesangial cells: it suggests that inhibition of this enzyme may be useful to prevented extracellular matrix (ECM) deposition in glomerulosclerosis.

Aldose reductase protects against early atherosclerotic lesion formation in apolipoprotein E-null mice

RATIONALE

Atherosclerotic lesion formation is associated with the accumulation of oxidized lipids. Products of lipid oxidation, particularly aldehydes, stimulate cytokine production and enhance monocyte adhesion; however, their contribution to atherosclerotic lesion formation remains unclear.

OBJECTIVE

To test the hypothesis that inhibition of aldehyde removal by aldose reductase (AR), which metabolizes both free and phospholipid aldehydes, exacerbates atherosclerotic lesion formation.

METHODS AND RESULTS

In atherosclerotic lesions of apolipoprotein (apo)E-null mice, AR protein was located in macrophage-rich regions and its abundance increased with lesion progression. Treatment of apoE-null mice with AR inhibitors sorbinil or tolrestat increased early lesion formation but did not affect the formation of advanced lesions. Early lesions of AR(-/-)/apoE(-/-) mice maintained on high-fat diet were significantly larger when compared with age-matched AR(+/+)/apoE(-/-) mice. The increase in lesion area attributable to deletion of the AR gene was seen in both male and female mice. Pharmacological inhibition or genetic ablation of AR also increased the lesion formation in male mice made diabetic by streptozotocin treatment. Lesions in AR(-/-)/apoE(-/-) mice exhibited increased collagen and macrophage content and a decrease in smooth muscle cells. AR(-/-)/apoE(-/-) mice displayed a greater accumulation of the AR substrate 4-hydroxy trans-2-nonenal (HNE) in the plasma and protein-HNE adducts in arterial lesions than AR(+/+)/apoE(-/-) mice.

CONCLUSIONS

These observations indicate that AR is upregulated in atherosclerotic lesions and it protects against early stages of atherogenesis by removing toxic aldehydes generated in oxidized lipids.

Characterization of two novel aldo-keto reductases from Arabidopsis: expression patterns, broad substrate specificity, and an open active-site structure suggest a role in toxicant metabolism following stress

Aldo-keto reductases (AKRs) are widely distributed in nature and play numerous roles in the metabolism of steroids, sugars, and other carbonyls. They have also frequently been implicated in the metabolism of exogenous and endogenous toxicants, including those stimulated by stress. Although the Arabidopsis genome includes at least 21 genes with the AKR signature, very little is known of their functions. In this study, we have screened the Arabidopsis thaliana genomic sequence for genes with significant homology to members of the mammalian AKR1 family and identified four homologues for further study. Following alignment of the predicted protein sequences with representatives from the AKR superfamily, the proteins were ascribed not to the AKR1 family but to the AKR4C subfamily, with the individual designations of AKR4C8, AKR4C9, AKR4C10, and AKR4C11. Expression of two of the genes, AKR4C8 and AKR4C9, has been shown to be coordinately regulated and markedly induced by various forms of stress. The genes have been overexpressed in bacteria, and recombinant proteins have been purified and crystallized. Both enzymes display NADPH-dependent reduction of carbonyl compounds, typical of the superfamily, but will accept a very wide range of substrates, reducing a range of steroids, sugars, and aliphatic and aromatic aldehydes/ketones, although there are distinct differences between the two enzymes. We have obtained high-resolution crystal structures of AKR4C8 (1.4 A) and AKR4C9 (1.25 A) in ternary complexes with NADP(+) and acetate. Three extended loops, present in all AKRs and responsible for defining the cofactor- and substrate-binding sites, are shorter in the 4C subfamily compared to other AKRs. Consequently, the crystal structures reveal open and accommodative substrate-binding sites, which correlates with their broad substrate specificity. It is suggested that the primary role of these enzymes may be to detoxify a range of toxic aldehydes and ketones produced during stress, although the precise nature of the principal natural substrates remains to be determined.

Kinetic studies of AKR1B10, human aldose reductase-like protein: endogenous substrates and inhibition by steroids

A human member of the aldo-keto reductase (AKR) superfamily, AKR1B10, was identified as a biomarker of lung cancer, exhibiting high sequence identity with human aldose reductase (AKR1B1). Using recombinant AKR1B10 and AKR1B1, we compared their substrate specificity for biogenic compounds and inhibition by endogenous compounds and found the following unique features of AKR1B10. AKR1B10 efficiently reduced long-chain aliphatic aldehydes including farnesal and geranylgeranial, which are generated from degradation of prenylated proteins and metabolism of farnesol and geranylgeraniol derived from the mevalonate pathway. The enzyme oxidized aliphatic and aromatic alcohols including 20alpha-hydroxysteroids. In addition, AKR1B10 was inhibited by steroid hormones, bile acids and their metabolites, showing IC(50) values of 0.03-25 microM. Kinetic analyses of the alcohol oxidation and inhibition by the steroids and tolrestat, together with the docked model of AKR1B10-inhibitor complex, suggest that the inhibitory steroids and tolrestat bind to overlapping sites within the active site of the enzyme-coenzyme complex. Thus, we propose a novel role of AKR1B10 in controlling isoprenoid homeostasis that is important in cholesterol synthesis and cell proliferation through salvaging isoprenoid alcohols, as well as its metabolic regulation by endogenous steroids.

Posttranslational glutathiolation of aldose reductase (AKR1B1): a possible mechanism of protein recovery from S-nitrosylation

Nitric oxide (NO) is an important regulator of the catalytic activity of aldose reductase (AR). It reacts with the active site cysteines of AR and this reaction results in the formation of several kinetically distinct forms of the protein. The catalytic activity of AR is increased in the ischemic heart and this increase in activity is associated with NO-dependent modification of AR. During reperfusion, the enzyme reverts back to its un-activated form. Although, AR activation has been linked to thiol oxidation, the mechanisms of de-activation remain unclear. Here we report that treatment of recombinant human AR (AKR1B1) by a non-thiol-based NO-donor (DEANO) results in activation and S-nitrosylation of the protein. The nitrosylated (ARSNO), but not the reduced (ARSH), protein reacted with reduced glutathione (GSH) and this reaction resulted in the formation of glutathiolated AR (ARSSG). The modification of AR by NO was site-specific at Cys-298 and was not affected by selective mutation of the neighboring residue, Cys-303 to an alanine. Incubation of the glutathiolated AR (ARSSG) with GSH resulted in the regeneration of the reduced form of the protein (ARSH). Treatment of nitrosylated AR (ARSNO) with ascorbic acid also led to the conversion of the protein to its reduced form. These observations suggest that intracellular reductants such as GSH and ascorbate could convert the nitrosylated form of AR to its basal or reduced state. In general, such reductive reactions might represent a common mechanism for denitrosylating proteins or an "off" switch in NO-mediated signaling pathways involving protein S-nitrosylation reactions.

The role of iron in the pathogenesis of endometriosis

BACKGROUND

Endometriosis may cause symptoms including chronic pelvic pain and infertility, and increases susceptibility to the development of ovarian cancer. Genomic studies have started to delineate the wide array of mediators involved in the development of endometriosis. Understanding the mechanisms of endometriosis development and elucidating its pathogenesis and pathophysiology are intrinsic to prevention and the search for effective therapies.

METHOD OF STUDY

The present article reviews the English language literature for biological, pathogenetic and pathophysiological studies on endometriosis. Several recent genomic studies are discussed in the context of endometriosis biology.

RESULTS

Severe hemolysis occurring during the development of endometriosis results in high levels of free heme and iron. These compounds oxidatively modify lipids and proteins, leading to cell and DNA damage, and subsequently fibrosis development. Recent studies based on genome-wide expression analysis technology have noted specific expression of heme/iron-dependent mediators in endometriosis. The heme/iron-dependent signaling pathway of endometriosis, which is providing new insights into the regulation of inflammation, detoxification and survival, is discussed.

CONCLUSION

Several important endometriosis-specific genes overlap with those known to be regulated by iron. Other genes are involved in oxidative stress. Iron has a significant impact on endometriotic-cell gene expression. This review summarizes recent advances in the heme/iron-mediated signaling and its target genes, outlines the potential challenges to understanding of the pathogenesis and pathophysiology of endometriosis, and proposes a possible novel model.

Correlation of binding constants and molecular modelling of inhibitors in the active sites of aldose reductase and aldehyde reductase

Aldose reductase (ALR2) belongs to the aldo-keto reductase (AKR) superfamily of enzymes, is the first enzyme involved in the polyol pathway of glucose metabolism and has been linked to the pathologies associated with diabetes. Molecular modelling studies together with binding constant measurements for the four inhibitors Tolrestat, Minalrestat, quercetin and 3,5-dichlorosalicylic acid (DCL) were used to determine the type of inhibition, and correlate inhibitor potency and binding energies of the complexes with ALR2 and the homologous aldehyde reductase (ALR1), another member of the AKR superfamily. Our results show that the four inhibitors follow either uncompetitive or non-competitive inhibition pattern of substrate reduction for ALR1 and ALR2. Overall, there is correlation between the IC(50) (concentration giving 50% inhibition) values of the inhibitors for the two enzymes and the binding energies (DeltaH) of the enzyme-inhibitor complexes. Additionally, the results agree with the detailed structural information obtained by X-ray crystallography suggesting that the difference in inhibitor binding for the two enzymes is predominantly mediated by non-conserved residues. In particular, Arg312 in ALR1 (missing in ALR2) contributes favourably to the binding of DCL through an electrostatic interaction with the inhibitor's electronegative halide atom and undergoes a conformational change upon Tolrestat binding. In ALR2, Thr113 (Tyr116 in ALR1) forms electrostatic interactions with the fluorobenzyl moiety of Minalrestat and the 3- and 4-hydroxy groups on the phenyl ring of quercetin. Our modelling studies suggest that Minalrestat's binding to ALR1 is accompanied by a conformational change including the side chain of Tyr116 to achieve the selectivity for ALR1 over ALR2.

Arsenic and cardiovascular disease

Chronic arsenic exposure is a worldwide health problem. Although arsenic-induced cancer has been widely studied, comparatively little attention has been paid to arsenic-induced vascular disease. Epidemiological studies have shown that chronic arsenic exposure is associated with increased morbidity and mortality from cardiovascular disease. In addition, studies suggest that susceptibility to arsenic-induced vascular disease may be modified by nutritional factors in addition to genetic factors. Recently, animal models for arsenic-induced atherosclerosis and liver sinusoidal endothelial cell dysfunction have been developed. Initial studies in these models show that arsenic exposure accelerates and exacerbates atherosclerosis in apolipoprotein E-knockout mice. Microarray studies of liver mRNA and micro-RNA abundance in mice exposed in utero suggest that a permanent state of stress is induced by the arsenic exposure. Furthermore, the livers of the arsenic-exposed mice have activated pathways involved in immune responses suggesting a pro-hyperinflammatory state. Arsenic exposure of mice after weaning shows a clear dose-response in the extent of disease exacerbation. In addition, increased inflammation in arterial wall is evident. In response to arsenic-stimulated oxidative signaling, liver sinusoidal endothelium differentiates into a continuous endothelium that limits nutrient exchange and waste elimination. Data suggest that nicotinamide adenine dinucleotide phosphate oxidase-derived superoxide or its derivatives are essential second messengers in the signaling pathway for arsenic-stimulated vessel remodeling. The recent findings provide future directions for research into the cardiovascular effects of arsenic exposure.

Aldose reductase decreases endoplasmic reticulum stress in ischemic hearts

Aldose reductase (AR) is a multi-functional AKR (AKR1B1) that catalyzes the reduction of a wide range of endogenous and xenobiotic aldehydes and their glutathione conjugates with high efficiency. Previous studies from our laboratory show that AR protects against myocardial ischemia-reperfusion injury, however, the mechanisms by which it confers cardioprotection remain unknown. Because AR metabolizes aldehydes generated from lipid peroxidation, we tested the hypothesis that it protects against ischemic injury by preventing ER stress induced by excessive accumulation of aldehyde-modified proteins in the ischemic heart. In cell culture experiments, exposure to model lipid peroxidation aldehydes-4-hydroxy-trans-2-nonenal (HNE), 1-palmitoyl-2-oxovaleroyl phosphatidylcholine (POVPC) or acrolein led to an increase in the phosphorylation of ER stress markers PERK and eIF2-alpha and an increase in ATF3. The reduced metabolite of POVPC 1-palmitoyl-2-hydroxyvaleroyl phosphatidylcholine (PHVPC) was unable to stimulate JNK phosphorylation. No increase in phospho-eIF2-alpha, ATF3 or phospho-PERK was observed in cells treated with the reduced HNE metabolite 1,4-dihydroxynonenol (DHN). Lysates prepared from isolated perfused mouse hearts subjected to 15 min of global ischemia followed by 30 min of reperfusion ex vivo showed greater phosphorylation of PERK and eIF2-alpha than hearts subjected to aerobic perfusion alone. Ischemia-induced increases in phospho-PERK and phospho-eIF2-alpha were diminished in the hearts of cardiomyocyte-specific transgenic mice overexpressing the AR transgene. These observations support the notion that by removing aldehydic products of lipid peroxidation, AR decreases ischemia-reperfusion injury by diminishing ER stress.

Structure of aldehyde reductase in ternary complex with coenzyme and the potent 20alpha-hydroxysteroid dehydrogenase inhibitor 3,5-dichlorosalicylic acid: implications for inhibitor binding and selectivity

The structure of aldehyde reductase (ALR1) in ternary complex with the coenzyme NADPH and 3,5-dichlorosalicylic acid (DCL), a potent inhibitor of human 20alpha-hydroxysteroid dehydrogenase (AKR1C1), was determined at a resolution of 2.41A. The inhibitor formed a network of hydrogen bonds with the active site residues Trp22, Tyr50, His113, Trp114 and Arg312. Molecular modelling calculations together with inhibitory activity measurements indicated that DCL was a less potent inhibitor of ALR1 (256-fold) when compared to AKR1C1. In AKR1C1, the inhibitor formed a 10-fold stronger binding interaction with the catalytic residue (Tyr55), non-conserved hydrogen bonding interaction with His222, and additional van der Waals contacts with the non-conserved C-terminal residues Leu306, Leu308 and Phe311 that contribute to the inhibitor's selectivity advantage for AKR1C1 over ALR1.

Catalytic mechanism and substrate specificity of the beta-subunit of the voltage-gated potassium channel

The beta-subunits of voltage-gated potassium (Kv) channels are members of the aldo-keto reductase (AKR) superfamily. These proteins regulate inactivation and membrane localization of Kv1 and Kv4 channels. The Kvbeta proteins bind to pyridine nucleotides with high affinity; however, their catalytic properties remain unclear. Here we report that recombinant rat Kvbeta2 catalyzes the reduction of a wide range of aldehydes and ketones. The rate of catalysis was slower (0.06-0.2 min(-1)) than those of most other AKRs but displayed the expected hyperbolic dependence on substrate concentration, with no evidence of allosteric cooperativity. Catalysis was prevented by site-directed substitution of Tyr-90 with phenylalanine, indicating that the acid-base catalytic residue, identified in other AKRs, has a conserved function in Kvbeta2. The protein catalyzed the reduction of a broad range of carbonyls, including aromatic carbonyls, electrophilic aldehydes and prostaglandins, phospholipids, and sugar aldehydes. Little or no activity was detected with carbonyl steroids. Initial velocity profiles were consistent with an ordered bi-bi rapid equilibrium mechanism in which NADPH binding precedes carbonyl binding. Significant primary kinetic isotope effects (2.0-3.1) were observed under single- and multiple-turnover conditions, indicating that the bond-breaking chemical step is rate-limiting. Structure-activity relationships with a series of para-substituted benzaldehydes indicated that the electronic interactions predominate during substrate binding and that no significant charge develops during the transition state. These data strengthen the view that Kvbeta proteins are catalytically active AKRs that impart redox sensitivity to Kv channels.

The responses of mitochondrial proteome in rat liver to the consumption of moderate ethanol: the possible roles of aldo-keto reductases

A large body of evidence supports the view that mitochondria are a primary target of alcohol stress. Changes in mitochondrial proteins due to moderate ethanol intake, however, have not been broadly and accurately estimated. For this study, rats were fed low doses of ethanol and the mitochondria were isolated from heart, kidney, and liver, using ultracentrifugation with Nycodenz density gradient. The mitochondrial proteins were well resolved upon two-dimensional electrophoresis (2DE), and the alcohol-responsive 2DE spots were identified by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF/TOF MS). Compared with the control group, the proteins extracted from liver mitochondria of ethanol-fed rats exhibited the significant changes on 2DE images, whereas the 2DE images obtained from the kidney and the heart mitochondria remained almost unchanged by ethanol feeding. Significantly, over 50% of the alcohol-responsive proteins in liver mitochondria were members of aldo-keto reductase family (AKR), which were usually present in cytoplasm. The organelle distributions of AKR proteins in liver mitochondria were further confirmed by Western blot analysis as well as by confocal microscopy. In addition, translocations of AKR were examined in the CHANG cell line, which was cultured with and without ethanol. The results of Western blot strongly suggested that the abundances of AKR proteins in the mitochondria were greatly reduced by the presence of ethanol in culture medium. The results of this study show that, even with moderate ethanol feeding, the mitochondrial proteome in rat liver was more sensitive to alcohol stress than that of either the kidney or the heart. The translocation of AKR proteins may be involved in the detoxification of liver cells.

Role of nitric oxide in regulating aldose reductase activation in the ischemic heart

Aldose reductase (AR) catalyzes the reduction of several aldehydes ranging from lipid peroxidation products to glucose. The activity of AR is increased in the ischemic heart due to oxidation of its cysteine residues, but the underlying mechanisms remain unclear. To examine signaling mechanisms regulating AR activation, we studied the role of nitric oxide (NO). Treatment with the NO synthase (NOS) inhibitor, N-nitro-l-arginine methyl ester prevented ischemia-induced AR activation and myocardial sorbitol accumulation in rat hearts subjected to global ischemia ex vivo or coronary ligation in situ, whereas inhibition of inducible NOS and neuronal NOS had no effect. Activation of AR in the ischemic heart was abolished by pretreatment with peroxynitrite scavengers hesperetin or 5, 10, 15, 20-tetrakis-[4-sulfonatophenyl]-porphyrinato-iron [III]. Site-directed mutagenesis and electrospray ionization mass spectrometry analyses showed that Cys-298 of AR was readily oxidized to sulfenic acid by peroxynitrite. Treatment with bradykinin and insulin led to a phosphatidylinositol 3-kinase (PI3K)-dependent increase in the phosphorylation of endothelial NOS at Ser-1177 and, even in the absence of ischemia, was sufficient in activating AR. Activation of AR by bradykinin and insulin was reversed upon reduction with dithiothreitol or by inhibiting NOS or PI3K. Treatment with AR inhibitors sorbinil or tolrestat reduced post-ischemic recovery in the rat hearts subjected to global ischemia and increased the infarct size when given before ischemia or upon reperfusion. These results suggest that AR is a cardioprotective protein and that its activation in the ischemic heart is due to peroxynitrite-mediated oxidation of Cys-298 to sulfenic acid via the PI3K/Akt/endothelial NOS pathway.

Unsaturated lipid peroxidation-derived aldehydes activate autophagy in vascular smooth-muscle cells

Proteins modified by aldehydes generated from oxidized lipids accumulate in cells during oxidative stress and are commonly detected in diseased or aged tissue. The mechanisms by which cells remove aldehyde-adducted proteins, however, remain unclear. Here, we report that products of lipid peroxidation such as 4-HNE (4-hydroxynonenal) and acrolein activate autophagy in rat aortic smooth-muscle cells in culture. Exposure to 4-HNE led to the modification of several proteins, as detected by anti-protein–4-HNE antibodies or protein-bound radioactivity in [3H]4-HNE-treated cells. The 4-HNE-modified proteins were gradually removed from cells. The removal of 4-HNE-modified proteins was not affected by the oxidized protein hydrolase inhibitor, acetyl leucine chloromethyl ketone, or lactacystin, although it was significantly decreased by PSI (proteasome inhibitor I), the lysosome/proteasome inhibitor MG-132 (carbobenzoxy-L-leucyl-L-leucyl-leucinal), insulin or the autophagy inhibitor 3-MA (3-methyladenine). Pre-incubation of cells with rapamycin accelerated the removal of 4-HNE-modified proteins. Treatment with 4-HNE, nonenal and acrolein, but not nonanal or POVPC (1-palmitoyl-2-oxovaleroyl phosphatidyl choline), caused a robust increase in LC3-II (microtubule-associated protein 1 light chain 3-II) formation, which was increased also by rapamycin, but prevented by insulin. Electron micrographs of 4-HNE-treated cells showed extensive vacuolization, pinocytic body formation, crescent-shaped phagophores, and multilamellar vesicles. Treatment with 3-MA and MG-132, but not proteasome-specific inhibitors, induced cell death in 4-HNE-treated cells. Collectively, these results show that lipid peroxidation-derived aldehydes stimulate autophagy, which removes aldehyde-modified proteins, and that inhibition of autophagy precipitates cell death in aldehyde-treated cells. Autophagy may be an important mechanism for the survival of arterial smooth-muscle cells under conditions associated with excessive lipid peroxidation.

The aldo-keto reductase superfamily and its role in drug metabolism and detoxification

The aldo-keto reductase (AKR) superfamily comprises enzymes that catalyze redox transformations involved in biosynthesis, intermediary metabolism, and detoxification. Substrates of AKRs include glucose, steroids, glycosylation end-products, lipid peroxidation products, and environmental pollutants. These proteins adopt a (beta/alpha)(8) barrel structural motif interrupted by a number of extraneous loops and helixes that vary between proteins and bring structural identity to individual families. The human AKR family differs from the rodent families. Due to their broad substrate specificity, AKRs play an important role in the phase II detoxification of a large number of pharmaceuticals, drugs, and xenobiotics.

Substrate specificity and catalytic efficiency of aldo-keto reductases with phospholipid aldehydes

Phospholipid oxidation generates several bioactive aldehydes that remain esterified to the glycerol backbone ('core' aldehydes). These aldehydes induce endothelial cells to produce monocyte chemotactic factors and enhance monocyte-endothelium adhesion. They also serve as ligands of scavenger receptors for the uptake of oxidized lipoproteins or apoptotic cells. The biochemical pathways involved in phospholipid aldehyde metabolism, however, remain largely unknown. In the present study, we have examined the efficacy of the three mammalian AKR (aldo-keto reductase) families in catalysing the reduction of phospholipid aldehydes. The model phospholipid aldehyde POVPC [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine] was efficiently reduced by members of the AKR1, but not by the AKR6 or the ARK7 family. In the AKR1 family, POVPC reductase activity was limited to AKR1A and B. No significant activity was observed with AKR1C enzymes. Among the active proteins, human AR (aldose reductase) (AKR1B1) showed the highest catalytic activity. The catalytic efficiency of human small intestinal AR (AKR1B10) was comparable with the murine AKR1B proteins 1B3 and 1B8. Among the murine proteins AKR1A4 and AKR1B7 showed appreciably lower catalytic activity as compared with 1B3 and 1B8. The human AKRs, 1B1 and 1B10, and the murine proteins, 1B3 and 1B8, also reduced C-7 and C-9 sn-2 aldehydes as well as POVPE [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphoethanolamine]. AKR1A4, B1, B7 and B8 catalysed the reduction of aldehydes generated in oxidized C(16:0-20:4) phosphatidylcholine with acyl, plasmenyl or alkyl linkage at the sn-1 position or C(16:0-20:4) phosphatidylglycerol or phosphatidic acid. AKR1B1 displayed the highest activity with phosphatidic acids; AKR1A4 was more efficient with long-chain aldehydes such as 5-hydroxy-8-oxo-6-octenoyl derivatives, whereas AKR1B8 preferred phosphatidylglycerol. These results suggest that proteins of the AKR1A and B families are efficient phospholipid aldehyde reductases, with non-overlapping substrate specificity, and may be involved in tissue-specific metabolism of endogenous or dietary phospholipid aldehydes.

Oxidized phospholipids: From molecular properties to disease

Oxidized lipids are generated from (poly)unsaturated diacyl- and alk(en)ylacyl glycerophospholipids under conditions of oxidative stress. The great variety of reaction products is defined by the degree of modification, hydrophobicity, chemical reactivity, physical properties and biological activity. The biological activities of these compounds may depend on both, the recognition of the particular molecular structures by specific receptors and on the unspecific physical and chemical effects on their target systems (membranes, proteins). In this review, we aim at highlighting the molecular features that are essential for the understanding of the biological actions of pure oxidized phospholipids. Firstly, their chemical structures are described as a basis for an understanding of their physical and (bio)chemical properties in membrane- and protein-bound form. Secondly, the biological activities of oxidized phospholipids are discussed in terms of their unspecific effects on the membrane level as well as their potential interactions with specific targets (receptors) affecting a large set of (signaling) molecules. Finally, the role of oxidized phospholipids as important mediators in pathophysiology is discussed with emphasis on atherosclerosis.

Excretory-secretory proteome of larval Schistosoma mansoni and Echinostoma caproni, two parasites of Biomphalaria glabrata

Schistosoma mansoni and Echinostoma caproni are two trematode species that use different strategies (mimicry and immunosuppression, respectively) to interfere with the snail innate immune system. Parasites excretory-secretory (ES) products have been shown to play a key role in these host-parasite immune interactions. However, they remain largely uncharacterized in larval trematodes. We developed a global proteomic approach to characterize the ES proteome of S. mansoni and E. caproni primary sporocysts. In ES products of both parasites, we found proteins involved in reactive oxygen species scavenging, glycolysis, signalling or calcium binding (superoxide dismutase Cu/Zn; glutathione S-transferase; aldo-keto-reductase; triose-phosphate isomerase; glyceraldehyde-3-phosphate dehydrogenase; aldolase, enolase, MICAL-like, calreticulin). According to their predicted functions, we propose a model in which these proteins (i) are involved in antioxidant activity, (ii) prevent hemocyte encapsulation process or (iii) favor invasion and migration of sporocysts in host tissues. These results suggest that S. mansoni and E. caproni sporocysts develope a strong immune protection during the first hours of infection giving them enough time to build up a long lasting immune evasion strategy relying on molecular mimicry or immunosuppression, respectively.

Nrf2 Gene Transfer Induces Antioxidant Enzymes and Suppresses Smooth Muscle Cell Growth In Vitro and Reduces Oxidative Stress in Rabbit Aorta In Vivo

Background— Reactive oxygen species (ROS) play a major role in vascular inflammation and pathophysiology of many vascular diseases such as atherosclerosis and injury-induced neointima formation after balloon angioplasty. Nuclear factor E2–related factor-2 (Nrf2) is a transcription factor orchestrating antioxidant and cytoprotective responses on oxidative and electrophilic stress, and it has been shown to have antiinflammatory effects in vascular cells in vitro. We therefore postulated that Nrf2 gene transfer would have salutary effects on vascular inflammation after angioplasty.

Methods and Results— Transduction of vascular smooth muscle cells (VSMCs) with Nrf2-expressing adenovirus increased the expression of several antioxidant enzymes including heme oxygenase-1 (HO-1) compared with β-galactosidase (AdLacZ)-transduced controls. Moreover, Nrf2 gene transfer also inhibited vascular smooth muscle cell (VSMC) proliferation, and the effect was partially reversed by the HO inhibitor Sn(IV) protoporphyrin. In vivo, adenoviral gene transfer effectively reduced oxidative stress determined by antibody staining against oxidized epitopes of LDL, as well as inhibited vascular inflammation assessed by the macrophage cell count and monocyte chemoattractant protein-1 (MCP-1) staining. However, the antiproliferative effects of Nrf2 in vivo were counterbalanced with diminished apoptosis in neointimal VSMCs, resulting in no change in neointimal hyperplasia.

Conclusions— Nrf2 gene transfer or Nrf2-inducing drugs may have therapeutic applications in vascular diseases in which inflammation and oxidative stress play a role. However, the contrasting growth inhibitory and antiapoptotic effects of Nrf2 need to be considered in pathological conditions in which SMC proliferation plays a critical role.

Endotoxin-induced cardiomyopathy and systemic inflammation in mice is prevented by aldose reductase inhibition

BACKGROUND

Sepsis is a systemic inflammatory response syndrome characterized by excessive production of inflammatory cytokines and cardiovascular collapse. Postreceptor signaling events that lead to stress responses and cytokine production are sensitive to redox changes and products of lipid peroxidation.

METHODS AND RESULTS

We tested the hypothesis that inflammatory signaling and cytokine generation during sepsis depend on the activity of the enzyme aldose reductase, which catalyzes the reduction of lipid peroxidation-derived aldehydes and their glutathione conjugates. The results of the present study show that pharmacological inhibition of aldose reductase by sorbinil or knockdown of the enzyme by small interfering RNA prevents the activation of nuclear factor-kappaB and the release of tumor necrosis factor-alpha from lipopolysaccharide-stimulated RAW264.7 or H9c2 cells. Increases in serum and cardiac cytokines in response to lipopolysaccharide challenge were suppressed by inhibition of aldose reductase. Treatment with sorbinil blunted the activation of protein kinase C, c-Jun NH2-terminal kinase, and p38, as well as phosphorylation of interleukin receptor-associated kinase, IkappaB-alpha, IkappaB kinase complex-alpha/beta, and phospholipase-gamma1 and -beta1. These changes were associated with decreased myocardial nuclear factor-kappaB and activating protein-1 activity, prostaglandin E2 production, induction of cyclooxygenase 2, and inducible nitric oxide synthase. Sorbinil treatment also induced functional recovery in myocardial fractional shortening in vivo and preserved contractile function of isolated perfused hearts. Inhibition of aldose reductase increased survival in mice injected with lethal doses of lipopolysaccharide.

CONCLUSIONS

The present demonstration that aldose reductase mediates endotoxin-induced inflammation and cardiomyopathy suggests that inhibition of this enzyme may be useful to attenuate maladaptive host responses and to treat acute cardiovascular dysfunction associated with endotoxic shock.

Structure of a glutathione conjugate bound to the active site of aldose reductase

Aldose reductase (AR) is a monomeric NADPH-dependent oxidoreductase that catalyzes the reduction of aldehydes, ketones, and aldo-sugars. AR has been linked to the development of hyperglycemic injury and is a clinical target for the treatment of secondary diabetic complications. In addition to reducing glucose, AR is key regulator of cell signaling through it's reduction of aldehydes derived from lipoproteins and membrane phospholipids. AR catalyzes the reduction of glutathione conjugates of unsaturated aldehydes with higher catalytic efficiency than free aldehydes. The X-ray structure of human AR holoenzyme in complex with the glutathione analogue S-(1,2-dicarboxyethyl) glutathione (DCEG) was determined at a resolution of 1.94 A. The distal carboxylate group of DCEG's dicarboxyethyl moiety interacted with the conserved AR anion binding site residues Tyr48, His110, and Trp111. The bound DCEG's glutathione backbone adopted the low-energy Y-shape form. The C-terminal carboxylate of DCEG glutathione's glycine formed hydrogen bonds to Leu301 and Ser302, while the remaining interactions between DCEG and AR were hydrophobic, permitting significant flexibility of the AR and glutathione (GS) analogue interaction. The observed conformation and interactions of DCEG with AR were consistent with our previously published molecular dynamics model of glutathionyl-propanal binding to AR. The current structure identifies major interactions of glutathione conjugates with the AR active-site residues.

1-O-alkyl-2-(ω-oxo)acyl-sn-glycerols from shark oil and human milk fat are potential precursors of PAF mimics and GHB

This study examines the feasibility that peroxidation and lipolysis of 1-O-alkyl-2,3-diacyl-sn-glycerols (DAGE) found in shark liver oil and human milk fat constitutes a potential source of dietary precursors of platelet activating factor (PAF) mimics and of gamma-hydroxybutyrate (GHB). Purified DAGE were converted into 1-O-alkyl-2-acyl-sn-glycerols by pancreatic lipase, without isomerization, and transformed into 1-O-alkyl-2-oxoacyl-sn-glycerols by mild autooxidation. The various core aldehydes without derivatization, as well as the corresponding dinitrophenylhydrazones, were characterized by chromatographic retention time and diagnostic ions by online electrospray mass spectrometry. Core aldehydes of oxidized shark liver oil yielded 23 molecular species of 1-O-alkyl-sn-glycerols with short-chain sn-2 oxoacyl groups, ranging from 4 to 13 carbons, some unsaturated. Autooxidation of human milk fat yielded 1-O-octadecyl-2-(9-oxo)nonanoyl-sn-glycerol, as the major core aldehyde. Because diradylglycerols with short fatty chains are absorbed in the intestine and react with cytidine diphosphate-choline in the enterocytes, it is concluded that formation of such PAF mimics as 1-O-alkyl-2-(omega-oxo)acyl-sn-glycerophosphocholine from unsaturated dietary DAGE is a realistic possibility. Likewise, a C4 core alcohol produced by aldol-keto reduction of a C4 core aldehyde constitutes a dietary precursor of the neuromodulator and recreational drug GHB, which has not been previously pointed out.