Regulation of aldose reductase and the polyol pathway activity by nitric oxide

Oxidative stress elicits the remodeling of vimentin filaments into biomolecular condensates

The intermediate filament protein vimentin performs an essential role in cytoskeletal interplay and dynamics, mechanosensing and cellular stress responses. In pathology, vimentin is a key player in tumorigenesis, fibrosis and infection. Vimentin filaments undergo distinct and versatile reorganizations, and behave as redox sensors. The vimentin monomer possesses a central α-helical rod domain flanked by N- and C-terminal low complexity domains. Interactions between this type of domains play an important function in the formation of phase-separated biomolecular condensates, which in turn are critical for the organization of cellular components. Here we show that several oxidants, including hydrogen peroxide and diamide, elicit the remodeling of vimentin filaments into small particles. Oxidative stress elicited by diamide induces a fast dissociation of filaments into circular, motile dots, which requires the presence of the single vimentin cysteine residue, C328. This effect is reversible, and filament reassembly can occur within minutes of oxidant removal. Diamide-elicited vimentin droplets recover fluorescence after photobleaching. Moreover, fusion of cells expressing differentially tagged vimentin allows the detection of dots positive for both tags, indicating that vimentin dots merge upon cell fusion. The aliphatic alcohol 1,6-hexanediol, known to alter interactions between low complexity domains, readily dissolves diamide-elicited vimentin dots at low concentrations, in a C328 dependent manner, and hampers reassembly. Taken together, these results indicate that vimentin oxidation promotes a fast and reversible filament remodeling into biomolecular condensate-like structures, and provide primary evidence of its regulated phase separation. Moreover, we hypothesize that filament to droplet transition could play a protective role against irreversible damage of the vimentin network by oxidative stress.

Influence of Nitrosyl Iron Complex with Thiosulfate Ligands on Therapeutically Important Targets Related to Type 2 Diabetes Mellitus

The high prevalence of type 2 diabetes mellitus (T2DM), and the lack of effective therapy, determine the need for new treatment options. The present study is focused on the NO-donors drug class as effective antidiabetic agents. Since numerous biological systems are involved in the pathogenesis and progression of T2DM, the most promising approach to the development of effective drugs for the treatment of T2DM is the search for pharmacologically active compounds that are selective for a number of therapeutic targets for T2DM and its complications: oxidative stress, non-enzymatic protein glycation, polyol pathway. The nitrosyl iron complex with thiosulfate ligands was studied in this work. Binuclear iron nitrosyl complexes are synthetic analogues of [2Fe-2S] centers in the regulatory protein natural reservoirs of NO. Due to their ability to release NO without additional activation under physiological conditions, these compounds are of considerable interest for the development of potential drugs. The present study explores the effects of tetranitrosyl iron complex with thiosulfate ligands (TNIC-ThS) on T2DM and its complications regarding therapeutic targets in vitro, as well as its ability to bind liposomal membrane, inhibit lipid peroxidation (LPO), and non-enzymatic glycation of bovine serum albumin (BSA), as well as aldose reductase, the enzyme that catalyzes the reduction in glucose to sorbitol in the polyol pathway. Using the fluorescent probe method, it has been shown that TNIC-ThS molecules interact with both hydrophilic and hydrophobic regions of model membranes. TNIC-ThS inhibits lipid peroxidation, exhibiting antiradical activity due to releasing NO (IC50 = 21.5 ± 3.7 µM). TNIC-ThS was found to show non-competitive inhibition of aldose reductase with Ki value of 5.25 × 10^-4 M. In addition, TNIC-ThS was shown to be an effective inhibitor of the process of non-enzymatic protein glycation in vitro (IC50 = 47.4 ± 7.6 µM). Thus, TNIC-ThS may be considered to contribute significantly to the treatment of T2DM and diabetic complications.

Computational Study of Asian Propolis Compounds as Potential Anti-Type 2 Diabetes Mellitus Agents by Using Inverse Virtual Screening with the DIA-DB Web Server, Tanimoto Similarity Analysis, and Molecular Dynamic Simulation

Propolis contains a wide range of pharmacological activities because of their various bioactive compounds. The beneficial effect of propolis is interesting for treating type-2 diabetes mellitus (T2DM) owing to dysregulation of multiple metabolic processes. In this study, 275 of 658 Asian propolis compounds were evaluated as potential anti-T2DM agents using the DIA-DB web server towards 18 known anti-diabetes protein targets. More than 20% of all compounds could bind to more than five diabetes targets with high binding affinity (<−9.0 kcal/mol). Filtering with physicochemical and pharmacokinetic properties, including ADMET parameters, 12 compounds were identified as potential anti-T2DM with favorable ADMET properties. Six of those compounds, (2R)-7,4′-dihydroxy-5-methoxy-8-methylflavone; (RR)-(+)-3′-senecioylkhellactone; 2′,4′,6′-trihydroxy chalcone; alpinetin; pinobanksin-3-O-butyrate; and pinocembrin-5-methyl ether were first reported as anti-T2DM agents. We identified the significant T2DM targets of Asian propolis, namely retinol-binding protein-4 (RBP4) and aldose reductase (AKR1B1) that have important roles in insulin sensitivity and diabetes complication, respectively. Molecular dynamic simulations showed stable interaction of selected propolis compounds in the active site of RBP4 and AKR1B1. These findings suggest that Asian propolis compound may be effective for treatment of T2DM by targeting RBP4 and AKR1B1.

Protein Lipoxidation: Basic Concepts and Emerging Roles

Protein lipoxidation is a non-enzymatic post-translational modification that consists of the covalent addition of reactive lipid species to proteins. This occurs under basal conditions but increases in situations associated with oxidative stress. Protein targets for lipoxidation include metabolic and signalling enzymes, cytoskeletal proteins, and transcription factors, among others. There is strong evidence for the involvement of protein lipoxidation in disease, including atherosclerosis, neurodegeneration, and cancer. Nevertheless, the involvement of lipoxidation in cellular regulatory mechanisms is less understood. Here we review basic aspects of protein lipoxidation and discuss several features that could support its role in cell signalling, including its selectivity, reversibility, and possibilities for regulation at the levels of the generation and/or detoxification of reactive lipids. Moreover, given the great structural variety of electrophilic lipid species, protein lipoxidation can contribute to the generation of multiple structurally and functionally diverse protein species. Finally, the nature of the lipoxidised proteins and residues provides a frameshift for a complex interplay with other post-translational modifications, including redox and redox-regulated modifications, such as oxidative modifications and phosphorylation, thus strengthening the importance of detailed knowledge of this process.

Type III intermediate filaments as targets and effectors of electrophiles and oxidants

Intermediate filaments (IFs) play key roles in cell mechanics, signaling and homeostasis. Their assembly and dynamics are finely regulated by posttranslational modifications. The type III IFs, vimentin, desmin, peripherin and glial fibrillary acidic protein (GFAP), are targets for diverse modifications by oxidants and electrophiles, for which their conserved cysteine residue emerges as a hot spot. Pathophysiological examples of these modifications include lipoxidation in cell senescence and rheumatoid arthritis, disulfide formation in cataracts and nitrosation in endothelial shear stress, although some oxidative modifications can also be detected under basal conditions. We previously proposed that cysteine residues of vimentin and GFAP act as sensors for oxidative and electrophilic stress, and as hinges influencing filament assembly. Accumulating evidence indicates that the structurally diverse cysteine modifications, either per se or in combination with other posttranslational modifications, elicit specific functional outcomes inducing distinct assemblies or network rearrangements, including filament stabilization, bundling or fragmentation. Cysteine-deficient mutants are protected from these alterations but show compromised cellular performance in network assembly and expansion, organelle positioning and aggresome formation, revealing the importance of this residue. Therefore, the high susceptibility to modification of the conserved cysteine of type III IFs and its cornerstone position in filament architecture sustains their role in redox sensing and integration of cellular responses. This has deep pathophysiological implications and supports the potential of this residue as a drug target.

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Type III intermediate filaments can be modified by many oxidants and electrophiles.

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Oxidative modifications of type III IFs occur in normal and pathological conditions.

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The conserved cysteine residue acts as a hub for redox/electrophilic modifications.

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Cysteine modifications elicit structure-dependent type III IF rearrangements.

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Type III intermediate filaments act as sensors for oxidative and electrophilic stress.

Insight into the cellular effects of nitrated phospholipids: Evidence for pleiotropic mechanisms of action

Nitrated phospholipids have been recently identified in biological systems and showed to display anti-oxidant and anti-inflammatory potential in models of inflammation in vitro. Here, we have explored the effects of nitrated 1-palmitoyl-2-oleyl-phosphatidyl choline (NO2-POPC) in cellular models. We have observed that NO2-POPC, but not POPC, induces cellular changes consisting in cytoskeletal rearrangement and cell shrinking, and ultimately, loss of cell adhesion or impaired cell attachment. NO2-POPC releases NO in vitro and induces accumulation of NO in cells. Nevertheless, the effects of NO2-POPC are not superimposable with those of NO donors, which points to distinctive mechanisms of action. Notably, they show a stronger parallelism, although not complete overlap, with the effects of nitrated fatty acids. Interestingly, redistribution of vimentin by NO2-POPC is attenuated in a C328S mutant, thus indicating that this residue may be a target for direct or indirect modification in NO2-POPC-treated cells. Additionally, NO2-POPC interacts with several typical lipoxidation targets in vitro, including vimentin and PPARγ constructs, likely through cysteine residues. Therefore, nitrated phospholipids emerge as potential novel electrophilic lipid mediators with selective actions.

Mammalian Sulfur Amino Acid Metabolism: A Nexus Between Redox Regulation, Nutrition, Epigenetics, and Detoxification

SIGNIFICANCE

Transsulfuration allows conversion of methionine into cysteine using homocysteine (Hcy) as an intermediate. This pathway produces S-adenosylmethionine (AdoMet), a key metabolite for cell function, and provides 50% of the cysteine needed for hepatic glutathione synthesis. The route requires the intake of essential nutrients (e.g., methionine and vitamins) and is regulated by their availability. Transsulfuration presents multiple interconnections with epigenetics, adenosine triphosphate (ATP), and glutathione synthesis, polyol and pentose phosphate pathways, and detoxification that rely mostly in the exchange of substrates or products. Major hepatic diseases, rare diseases, and sensorineural disorders, among others that concur with oxidative stress, present impaired transsulfuration. Recent Advances: In contrast to the classical view, a nuclear branch of the pathway, potentiated under oxidative stress, is emerging. Several transsulfuration proteins regulate gene expression, suggesting moonlighting activities. In addition, abnormalities in Hcy metabolism link nutrition and hearing loss.

CRITICAL ISSUES

Knowledge about the crossregulation between pathways is mostly limited to the hepatic availability/removal of substrates and inhibitors. However, advances regarding protein-protein interactions involving oncogenes, identification of several post-translational modifications (PTMs), and putative moonlighting activities expand the potential impact of transsulfuration beyond methylations and Hcy.

FUTURE DIRECTIONS

Increasing the knowledge on transsulfuration outside the liver, understanding the protein-protein interaction networks involving these enzymes, the functional role of their PTMs, or the mechanisms controlling their nucleocytoplasmic shuttling may provide further insights into the pathophysiological implications of this pathway, allowing design of new therapeutic interventions. Antioxid. Redox Signal. 29, 408-452.

Asthma and allergic rhinitis associate with the rs2229542 variant that induces a p.Lys90Glu mutation and compromises AKR1B1 protein levels

Asthma and rhinitis are two of the main clinical manifestations of allergy, in which increased reactive oxygen or electrophilic species can play a pathogenic role. Aldose reductase (AKR1B1) is involved in aldehyde detoxification and redox balance. Recent evidence from animal models points to a role of AKR1B1 in asthma and rhinitis, but its involvement in human allergy has not been addressed. Here, the putative association of allergic rhinitis and asthma with AKR1B1 variants has been explored by analysis of single-strand variants on the AKR1B1 gene sequence in 526 healthy subjects and 515 patients with allergic rhinitis, 366 of whom also had asthma. We found that the rs2229542 variant, introducing the p.Lys90Glu mutation, was significantly more frequent in allergic patients than in healthy subjects. Additionally, in cells transfected with expression vectors carrying the wild-type or the p.Lys90Glu variant of AKR1B1, the mutant consistently attained lower protein levels than the wild-type and showed a compromised thermal stability. Taken together, our results show that the rs2229542 variant associates with asthma and rhinitis, and hampers AKR1B1 protein levels and stability. This unveils a connection between the genetic variability of aldose reductase and allergic processes.

The chlorite-based drug WF10 constantly reduces hemoglobin A1c values and improves glucose control in diabetes patients with severe foot syndrome

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The chlorite-based drug WF10 improved healing of foot wounds in diabetic patients.

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Infusion with WF10 markedly reduced HbA1c values in patients with diabetic foot syndrome.

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After administration of WF10 HbA1c values remained low over at least 8 to 12 weeks.

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The chlorite component of WF10 is known to inactivate efficiently cytotoxic hemoglobin forms.

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This treatment prevented below knee amputation in patients with diabetic foot syndrome.

Aims

The intravenous application of the chlorite-based drug solution WF10 is known to improve wound healing in patients with diabetic foot syndrome. In this retrospective study, we addressed the question, which effects are caused by this drug in patients with diabetic foot ulcers on the hemoglobin A1c value.

Methods

Patients received five consecutive daily infusions of WF10. Three patients received a second cycle of WF10, and one patient a third cycle.

Results

On a group of twelve patients with diabetic foot syndrome, WF10 gradually reduced the HbA1c values from a high-risk range (9.1 ± 1.6% (76 ± 13 mmol/mol)) into a low-risk range in all patients but one. These values remain low over at least 8 to 12 weeks after the administration of WF10. This drug improved also considerably wound healing processes in eleven patients.

Conclusions

The chlorite component of WF10 is known to inactivate efficiently free cytotoxic hemoglobin forms that might accumulate in peripheral blood after hemolysis and induces the removal of pre-damaged red blood cells from circulation. By these mechanisms WF10 diminished toxic effects of hemolysis, improved microcirculation and glucose consumption in affected tissues, and prevented, thus, below knee amputation.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Modification of cysteine residues by cyclopentenone prostaglandins: interplay with redox regulation of protein function

Cyclopentenone prostaglandins (cyPG) are endogenous lipid mediators involved in the resolution of inflammation and the regulation of cell proliferation and cellular redox status. Upon exogenous administration they have shown beneficial effects in models of inflammation and tissue injury, as well as potential antitumoral actions, which have raised a considerable interest in their study for the development of therapeutic tools. Due to their electrophilic nature, the best-known mechanism of action of these mediators is the covalent modification of proteins at cysteine residues through Michael addition. Identification of cyPG targets through proteomic approaches, including MS/MS analysis to pinpoint the modified residues, is proving critical to characterize their mechanisms of action. Among the targets of cyPG are proinflammatory transcription factors, proteins involved in cell defense, such as the regulator of the antioxidant response Keap1 and detoxifying enzymes like GST, and key signaling proteins like Ras proteins. Moreover, cyPG may interact with redox-active small molecules, such as glutathione and hydrogen sulfide. Much has been learned about cyPG in the past few years and this knowledge has also contributed to clarify both pharmacological actions and signaling mechanisms of these and other electrophilic lipids. Given the fact that many cyPG targets are involved in or are targets for redox regulation, there is a complex interplay with redox-induced modifications. Here we address the modification of protein cysteine residues by cyPG elucidated by proteomic studies, paying special attention to the interplay with redox signaling.

Bioinformatics analysis of diabetic retinopathy using functional protein sequences

Diabetic retinopathy is the leading cause of blindness among patients with diabetes mellitus. We evaluated the role of several proteins that are likely to be involved in diabetic retinopathy by employing multiple sequence alignment using ClustalW tool and constructed a phylogram tree using functional protein sequences extracted from NCBI. Phylogram was constructed using Neighbor-Joining Algorithm in bioinformatics approach. It was observed that aldose reductase and nitric oxide synthase are closely associated with diabetic retinopathy. It is likely that vascular endothelial growth factor, pro-inflammatory cytokines, advanced glycation end products, and adhesion molecules that also play a role in diabetic retinopathy may do so by modulating the activities of aldose reductase and nitric oxide synthase. These results imply that methods designed to normalize aldose reductase and nitric oxide synthase activities could be of significant benefit in the prevention and treatment of diabetic retinopathy.

Inhibitors of Advanced Glycation End Product Formation and Neurovascular Dysfunction in Experimental Diabetes

Advanced glycation and lipoxidation end products (AGEs/ALEs) have been implicated in the pathogenesis of the major microvascular complications of diabetes mellitus: nephropathy, neuropathy, and retinopathy. This article reviews the evidence regarding the peripheral nerve and its vascular supply. Most investigations done to assess the role of AGEs/ALEs in animal models of diabetic neuropathy have used aminoguanidine as a prototypic inhibitor. Preventive or intervention experiments have shown treatment benefits for motor and sensory nerve conduction velocity, autonomic nitrergic neurotransmission, nerve morphometry, and nerve blood flow. The latter depends on improvements in nitric oxide-mediated endothelium-dependent vasodilation and is responsible for conduction velocity improvements. A mechanistic interpretation of aminoguanidine's action in terms of AGE/ALE inhibition is made problematic by the relative lack of specificity. However, other unrelated compounds, such as pyridoxamine and pyridoxamine analogues, have recently been shown to have beneficial effects similar to aminoguanidine, as well as to improve pain-related measures of thermal hyperalgesia and tactile allodynia. These data also stress the importance of redox metal ion-catalyzed AGE/ALE formation. A further approach is to decrease substrate availability by reducing the elevated levels of hexose and triose phosphates found in diabetes. Benfotiamine is a transketolase activator that directs these substrates to the pentose phosphate pathway, thus reducing tissue AGEs. A similar spectrum of improvements in nerve and vascular function were noted when using benfotiamine in diabetic rats. Taken together, the data provide strong support for an important role for AGEs/ALEs in the etiology of diabetic neuropathy.

Vascular endothelial dysfunction in diabetic cardiomyopathy: pathogenesis and potential treatment targets

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy, a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. Pathogenesis of diabetic cardiomyopathy involves vascular endothelial cell dysfunction, as well as myocyte necrosis. Clinical trials have identified hyperglycemia as the key determinant in the development of chronic diabetic complications. Sustained hyperglycemia induces several biochemical changes including increased non-enzymatic glycation, sorbitol-myoinositol-mediated changes, redox potential alterations, and protein kinase C (PKC) activation, all of which have been implicated in diabetic cardiomyopathy. Other contributing metabolic abnormalities may include defective glucose transport, increased myocyte fatty acid uptake, and dysmetabolism. These biochemical changes manifest as hemodynamic alterations and structural changes that include capillary basement membrane (BM) thickening, interstitial fibrosis, and myocyte hypertrophy and necrosis. Diabetes-mediated biochemical anomalies show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Studies in both animal and human diabetes have shown alteration of several factors including vasoactive molecules that may be instrumental in mediating structural and functional deficits at both the early and the late stages of the disease. In this review, we will highlight some of the important vascular changes leading to diabetic cardiomyopathy and discuss the emerging potential therapeutic interventions.

Redox regulation: a new challenge for pharmacology

Redox signaling is evolving as a new field of biochemical and pharmacological research. Unlike oxidative stress which is characterized by a macroscopic shift in cellular redox potentials and usually accompanied by oxygen radical induced damage, redox regulation involves subtle and more chemically defined oxidations of short duration. Most important is the reductive component as a necessary part of a reversible regulatory process. Examples of redox regulation occur during early stages of the immune response, in hypoxia or in endothelial dysfunction. Persistent oxidative events together with a decline in the cellular reduction potential lead to oxidative stress as is seen in the pathophysiology of sepsis, reperfusion damage, atherosclerosis and diabetes. Oxidative signals involve superoxide and nitric oxide as the main players which form a system of oxidizing, nitrating or nitrosating species leading to posttranslational modifications of proteins. Modern techniques of immunohistochemistry and mass spectrometry allow a correlation of protein modification, e.g., disulfide, S-oxide, S-nitroso or nitrotyrosine formation, with enzyme activities and cellular responses. In this commentary, examples of the control of prostanoid synthesis by the NO/O2- system are described. Redox regulation represents an interesting challenge for the development of drugs that modulate the oxidative trigger mechanisms or enforce the reductive pathways.

Cellular and molecular targets of protein S-glutathiolation

Oxidative stress and reactive oxygen species play a major role in both normal and pathophysiologic cellular processes. Although many cellular constituents can be damaged by oxidant exposure, cysteine thiol groups are among the most readily oxidized moieties found within cells. To avoid potentially irreversible cysteine thiol oxidation, cells have developed multiple antioxidant defenses to preserve these moieties. Among these defenses, protein S-glutathiolation has emerged as an important mechanism, both in the maintenance of thiol stability during oxidant exposure and as a rapid and efficient mechanism regulating protein activity and cellular metabolic pathways. Here we review the known molecular targets of S-glutathiolation, with emphasis on the varying molecular effects of S-glutathiolation on different proteins.

Role of aldose reductase and oxidative damage in diabetes and the consequent potential for therapeutic options

Aldose reductase (AR) is widely expressed aldehyde-metabolizing enzyme. The reduction of glucose by the AR-catalyzed polyol pathway has been linked to the development of secondary diabetic complications. Although treatment with AR inhibitors has been shown to prevent tissue injury in animal models of diabetes, the clinical efficacy of these drugs remains to be established. Recent studies suggest that glucose may be an incidental substrate of AR, which appears to be more adept in catalyzing the reduction of a wide range of aldehydes generated from lipid peroxidation. Moreover, inhibition of the enzyme has been shown to increase inflammation-induced vascular oxidative stress and prevent myocardial protection associated with the late phase of ischemic preconditioning. On the basis of these studies, several investigators have ascribed an important antioxidant role to the enzyme. Additionally, ongoing work indicates that AR is a critical component of intracellular signaling, and inhibition of the enzyme prevents high glucose-, cytokine-, or growth factor-induced activation of protein kinase C and nuclear factor-kappa-binding protein. Thus, treatment with AR inhibitors prevents vascular smooth muscle cell growth and endothelial cell apoptosis in culture and inflammation and restenosis in vivo. Additional studies indicate that the antioxidant and signaling roles of AR are interlinked and that AR regulates protein kinase C and nuclear factor-kappaB via redox-sensitive mechanisms. These data underscore the need for reevaluating anti-AR interventions for the treatment of diabetic complications. Potentially, the development of newer drugs that selectively inhibit AR-mediated glucose metabolism and signaling, without affecting aldehyde detoxification, may be useful in preventing inflammation associated with the development of diabetic complications, particularly micro- and macrovascular diseases.