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

High expression of AKR1B10 predicts low risk of early tumor recurrence in patients with hepatitis B virus-related hepatocellular carcinoma

To clarify the relationship between aldo-keto reductase family 1 member B10 (AKR1B10) expression and early hepatocellular carcinoma (HCC) recurrence, this study detected AKR1B10 expression in tumor and adjacent non-tumor tissues from 110 patients with hepatitis B virus (HBV)-related HCC underwent liver resection and analyzed its correlations with clinicopathological characteristics and prognosis of these patients. Detected by quantitative reverse transcription polymerase chain reaction, AKR1B10 mRNA expression showed significantly higher in HCC tissues than in adjacent non-tumor tissues, with a low level in normal liver tissues. Similar results was confirmed at the protein level using immunohistochemistry and Western blotting. High AKR1B10 expression was negatively correlated with serum alpha-fetoprotein level and positively correlated with HBV-DNA level. Patients with high AKR1B10 expression had significantly higher disease-free survival than those with low expression within 2 years after liver resection. Multivariate analysis also confirmed high AKR1B10 expression to be a predictor of low risk of early HCC recurrence. In addition, high AKR1B10 expression was found to be a favorable factor of overall survival. These results suggest that AKR1B10 is involved in HBV-related hepatocarcinogenesis, but its high expression could predict low risk of early tumor recurrence in patients with HBV-related HCC after liver resection.

Diacetyl and related flavorant α-Diketones: Biotransformation, cellular interactions, and respiratory-tract toxicity

Exposure to diacetyl and related α-diketones causes respiratory-tract damage in humans and experimental animals. Chemical toxicity is often associated with covalent modification of cellular nucleophiles by electrophilic chemicals. Electrophilic α-diketones may covalently modify nucleophilic arginine residues in critical proteins and, thereby, produce the observed respiratory-tract pathology. The major pathway for the biotransformation of α-diketones is reduction to α-hydroxyketones (acyloins), which is catalyzed by NAD(P)H-dependent enzymes of the short-chain dehydrogenase/reductase (SDR) and the aldo-keto reductase (AKR) superfamilies. Reduction of α-diketones to the less electrophilic acyloins is a detoxication pathway for α-diketones. The pyruvate dehydrogenase complex may play a significant role in the biotransformation of diacetyl to CO₂. The interaction of toxic electrophilic chemicals with cellular nucleophiles can be predicted by the hard and soft, acids and bases (HSAB) principle. Application of the HSAB principle to the interactions of electrophilic α-diketones with cellular nucleophiles shows that α-diketones react preferentially with arginine residues. Furthermore, the respiratory-tract toxicity and the quantum-chemical reactivity parameters of diacetyl and replacement flavorant α-diketones are similar. Hence, the identified replacement flavorant α-diketones may pose a risk of flavorant-induced respiratory-tract toxicity. The calculated indices for the reaction of α-diketones with arginine support the hypothesis that modification of protein-bound arginine residues is a critical event in α-diketone-induced respiratory-tract toxicity.

Aldose reductase (AKR1B) deficiency promotes phagocytosis in bone marrow derived mouse macrophages

Macrophages are critical drivers of the immune response during infection and inflammation. The pathogenesis of several inflammatory conditions, such as diabetes, cancer and sepsis has been linked with aldose reductase (AR), a member of the aldo-keto reductase (AKR) superfamily. However, the role of AR in the early stages of innate immunity such as phagocytosis remains unclear. In this study, we examined the role of AR in regulating the growth and the phagocytic activity of bone marrow-derived mouse macrophages (BMMs) from AR-null and wild-type (WT) mice. We found that macrophages derived from AR-null mice were larger in size and had a slower growth rate than those derived from WT mice. The AR-null macrophages also displayed higher basal, and lipopolysaccharide (LPS) stimulated phagocytic activity than WT macrophages. Moreover, absence of AR led to a marked increase in cellular levels of both ATP and NADPH. These data suggest that metabolic pathways involving AR suppress macrophage energy production, and that inhibition of AR could induce a favorable metabolic state that promotes macrophage phagocytosis. Hence, modulation of macrophage metabolism by inhibition of AR might represent a novel strategy to modulate host defense responses and to modify metabolism to promote macrophage hypertrophy and phagocytosis under inflammatory conditions.

Aldo-Keto Reductase Family 1 Member B10 Inhibitors: Potential Drugs for Cancer Treatment

Cytosolic NADPH-dependent reductase AKR1B10 is a member of the aldo-keto reductase (AKR) superfamily. This enzyme is normally expressed in the gastrointestinal tract. However, it is overexpressed in many solid tumors, such as hepatocarcinoma, lung cancer and breast cancer. AKR1B10 may play a role in the formation and development of carcinomas through multiple mechanisms including detoxification of cytotoxic carbonyls, modulation of retinoic acid level, and regulation of cellular fatty acid synthesis and lipid metabolism. Studies have suggested that AKR1B10 may be a useful biomarker for cancer diagnosis and a potential target for cancer treatment. Over the last decade, a number of AKR1B10 inhibitors including aldose reductase inhibitors (ARIs), endogenous substances, natural-based derivatives and synthetic compounds have been developed, which could be novel anticancer drugs. This review provides an overview on related articles and patents about AKR1B10 inhibitors, with a focus on their inhibition selectivity and mechanism of function.

The Coptotermes gestroi aldo-keto reductase: a multipurpose enzyme for biorefinery applications

BACKGROUND

In nature, termites can be considered as a model biological system for biofuel research based on their remarkable efficiency for lignocellulosic biomass conversion. Redox enzymes are of interest in second-generation ethanol production because they promote synergic enzymatic activity with classical hydrolases for lignocellulose saccharification and inactivate fermentation inhibitory compounds produced after lignocellulose pretreatment steps.

RESULTS

In the present study, the biochemical and structural characteristics of the Coptotermes gestroi aldo-keto reductase (CgAKR-1) were comprehensively investigated. CgAKR-1 displayed major structural differences compared with others AKRs, including the differences in the amino acid composition of the substrate-binding site, providing basis for classification as a founding member of a new AKR subfamily (family AKR1 I). Immunolocalization assays with anti-CgAKR-1 antibodies resulted in strong fluorescence in the salivary gland, proventriculus, and foregut. CgAKR-1 supplementation caused a 32% reduction in phenolic aldehydes, such as furfural, which act as fermentation inhibitors of hemicellulosic hydrolysates, and improved ethanol fermentation by the xylose-fermenting yeast Scheffersomyces stipitis by 45%. We observed synergistic enzymatic interactions between CgAKR-1 and commercial cellulosic cocktail for sugarcane bagasse saccharification, with a maximum synergism degree of 2.17 for sugar release. Our data indicated that additive enzymatic activity could be mediated by reactive oxygen species because CgAKR-1 could produce hydrogen peroxide.

CONCLUSION

In summary, we identified the founding member of an AKRI subfamily with a potential role in the termite digestome. CgAKR-1 was found to be a multipurpose enzyme with potential biotechnological applications. The present work provided a basis for the development and application of integrative and multipurpose enzymes in the bioethanol production chain.

Correlated mutations in hydroxysteroid dehydrogenases family

Background

Hydroxysteroid dehydrogenase enzymes belong to the short-chain dehydrogenase/reductase (SDR) superfamily and aldo-keto reductases (AKRs). SDR is involved in the metabolism of many compounds (hormones, lipids, etc.) and is present in almost all studied genomes. Two hundred members of hydroxysteroid dehydrogenases have been analysed in terms of natural mutational variability. The second superfamily comprises AKR superfamily group enzymes whose function is catalysing the oxidation and reduction of many substrates by binding NAD(P)H as a cofactor. This kind of study is the first approach for the hydroxysteroid dehydrogenase family. This information grants practical meaning to designing potential specific drugs to fight specific diseases caused by mutations.

Methods

In the research, amino acid sequences of representatives of the hydroxysteroid dehydrogenase family were extracted from the UniProt database. In total, the analysed 200 sequences with the highest degree of similarity were shown by BLAST searches. In the sequence analyses, we used the following software: ClustalX (multiple sequence alignment), Consensus Constructor (creating consensus sequence), and CORM (finding correlated mutations).

Results

The CORM program identified potential sites of correlated mutations in hydroxysteroid dehydrogenases. This program generated 18 tables of results that contain the amino acid positions of mutations. Seven of these are presented in this paper.

Conclusions

The primary structure of the hydroxysteroid dehydrogenase family shows high variation.

Loss of Glyoxalase 1 Induces Compensatory Mechanism to Achieve Dicarbonyl Detoxification in Mammalian Schwann Cells

The glyoxalase system is a highly specific enzyme system existing in all mammalian cells that is responsible for the detoxification of dicarbonyl species, primarily methylglyoxal (MG). It has been implicated to play an essential role in preventing the increased formation of advanced glycation end products under certain pathological conditions. We have established the first glyoxalase 1 knock-out model (GLO1^-/-) in mammalian Schwann cells using the CRISPR/Cas9 technique to investigate compensatory mechanisms. Neither elevated concentrations of MG nor associated protein modifications were observed in GLO1^-/- cells. Alternative detoxification of MG in GLO1^-/- is achieved by increased catalytic efficiency of aldose reductase toward hemithioacetal (product of glutathione and MG), which is most likely caused by S-nitrosylation of aldose reductase. The hemithioacetal is mainly converted into lactaldehyde, which is paralleled by a loss of reduced glutathione. Inhibition of aldose reductase in GLO1^-/- cells is associated with an increased sensitivity against MG, elevated intracellular MG levels, associated modifications, as well as increased oxidative stress. Our data suggest that aldose reductase can compensate for the loss of GLO1. This might be of clinical importance within the context of neuronal diseases caused by an impaired glyoxalase system and elevated levels of dicarbonyl species, such as MG.

The identification of human aldo-keto reductase AKR7A2 as a novel cytoglobin-binding partner

Cytoglobin (CYGB), a member of the globin family, is thought to protect cells from reactive oxygen and nitrogen species and deal with hypoxic conditions and oxidative stress. However, its molecular mechanisms of action are not clearly understood. Through immunoprecipitation combined with a two-dimensional electrophoresis–mass spectrometry assay, we identified a CYGB interactor: aldo-keto reductase family 7 member A2 (AKR7A2). The interaction was further confirmed using yeast two-hybrid and co-immunoprecipitation assays. Our results show that AKR7A2 physically interacts with CYGB.

IDD388 Polyhalogenated Derivatives as Probes for an Improved Structure-Based Selectivity of AKR1B10 Inhibitors

Human enzyme aldo-keto reductase family member 1B10 (AKR1B10) has evolved as a tumor marker and promising antineoplastic target. It shares high structural similarity with the diabetes target enzyme aldose reductase (AR). Starting from the potent AR inhibitor IDD388, we have synthesized a series of derivatives bearing the same halophenoxyacetic acid moiety with an increasing number of bromine (Br) atoms on its aryl moiety. Next, by means of IC₅₀ measurements, X-ray crystallography, WaterMap analysis, and advanced binding free energy calculations with a quantum-mechanical (QM) approach, we have studied their structure-activity relationship (SAR) against both enzymes. The introduction of Br substituents decreases AR inhibition potency but improves it in the case of AKR1B10. Indeed, the Br atoms in ortho position may impede these drugs to fit into the AR prototypical specificity pocket. For AKR1B10, the smaller aryl moieties of MK181 and IDD388 can bind into the external loop A subpocket. Instead, the bulkier MK184, MK319, and MK204 open an inner specificity pocket in AKR1B10 characterized by a π-π stacking interaction of their aryl moieties and Trp112 side chain in the native conformation (not possible in AR). Among the three compounds, only MK204 can make a strong halogen bond with the protein (-4.4 kcal/mol, using QM calculations), while presenting the lowest desolvation cost among all the series, translated into the most selective and inhibitory potency AKR1B10 (IC₅₀ = 80 nM). Overall, SAR of these IDD388 polyhalogenated derivatives have unveiled several distinctive AKR1B10 features (shape, flexibility, hydration) that can be exploited to design novel types of AKR1B10 selective drugs.

Roles of aldo-keto reductases 1B10 and 1C3 and ATP-binding cassette transporter in docetaxel tolerance

Docetaxel (DTX) is widely used for treatment of inveterate lung and prostate cancers, but its continuous administration elicits the hyposensitivity. Here, we established the DTX-resistant variants of human lung cancer A549 and androgen-independent prostate cancer Du145 cells and found that the resistance development provoked aberrant up-regulations of aldo-keto reductase (AKR) 1B10 and AKR1C3 in A549 and Du145 cells, respectively. In addition, the sensitivity to the DTX toxicity was significantly decreased and increased by overexpression and knockdown of the two AKR isoforms, respectively. Furthermore, the resistant cells exhibited a decreased level of reactive 4-hydroxy-2-nonenal formed during DTX treatment, and the decrease was alleviated by adding the AKR inhibitors, inferring that the two AKRs confer the chemoresistance through elevating the antioxidant properties. The development of DTX resistance was also associated with enhanced expression of an ATP-binding cassette (ABC) transporter ABCB1 among the ABC transporter isoforms. The combined treatment with inhibitors of the two AKRs and ABCB1 additively sensitized the resistant cells to DTX. Intriguingly, the AKR1B10 inhibitor also suppressed the lung cancer cross-resistance against cisplatin. The results suggest that combined treatment with AKRs (1B10 and 1C3) and ABCB1 inhibitors exerts overcoming effect against the cancer resistance to DTX and cisplatin, and can be used as the adjuvant therapy.

Inhibition of aldo-keto reductase family 1 member B10 by unsaturated fatty acids

A human member of the aldo-keto reductase (AKR) superfamily, AKR1B10, is a cytosolic NADPH-dependent reductase toward various carbonyl compounds including reactive aldehydes, and is normally expressed in intestines. The enzyme is overexpressed in several extraintestinal cancers, and suggested as a potential target for cancer treatment. We found that saturated and cis-unsaturated fatty acids inhibit AKR1B10. Among the saturated fatty acids, myristic acid was the most potent, showing the IC₅₀ value of 4.2 μM cis-Unsaturated fatty acids inhibited AKR1B10 more potently, and linoleic, arachidonic, and docosahexaenoic acids showed the lowest IC₅₀ values of 1.1 μM. The inhibition by these fatty acids was reversible and kinetically competitive with respect to the substrate, showing the K_i values of 0.24-1.1 μM. These fatty acids, except for α-linoleic acid, were much less inhibitory to structurally similar aldose reductase. Site-directed mutagenesis study suggested that the fatty acids interact with several active site residues of AKR1B10, of which Gln114, Val301 and Gln303 are responsible for the inhibitory selectivity. Linoleic and arachidonic acids also effectively inhibited AKR1B10-mediated 4-oxo-2-nonenal metabolism in HCT-15 cells. Thus, the cis-unsaturated fatty acids may be used as an adjuvant therapy for treatment of cancers that up-regulate AKR1B10.

Extreme makeover: Engineering the activity of a thermostable alcohol dehydrogenase (AdhD) from Pyrococcus furiosus

Alcohol dehydrogenase D (AdhD) is a monomeric thermostable alcohol dehydrogenase from the aldo-keto reductase (AKR) superfamily of proteins. We have been exploring various strategies of engineering the activity of AdhD so that it could be employed in future biotechnology applications. Driven by insights made in other AKRs, we have made mutations in the cofactor-binding pocket of the enzyme and broadened its cofactor specificity. A pre-steady state kinetic analysis yielded new insights into the conformational behavior of this enzyme. The most active mutant enzyme concomitantly gained activity with a non-native cofactor, nicotinamide mononucleotide, NMN(H), and an enzymatic biofuel cell was demonstrated with this enzyme/cofactor pair. Substrate specificity was altered by grafting loop regions near the active site pocket from a mesostable human aldose reductase (hAR) onto the thermostable AdhD. These moves not only transferred the substrate specificity of hAR but also the cofactor specificity of hAR. We have added alpha-helical appendages to AdhD to enable it to self-assemble into a thermostable catalytic proteinaceous hydrogel. As our understanding of the structure/function relationship in AdhD and other AKRs advances, this ubiquitous protein scaffold could be engineered for a variety of catalytic activities that will be useful for many future applications.

Detoxifying Enzymes at the Cross-Roads of Inflammation, Oxidative Stress, and Drug Hypersensitivity: Role of Glutathione Transferase P1-1 and Aldose Reductase

Phase I and II enzymes are involved in the metabolism of endogenous reactive compounds as well as xenobiotics, including toxicants and drugs. Genotyping studies have established several drug metabolizing enzymes as markers for risk of drug hypersensitivity. However, other candidates are emerging that are involved in drug metabolism but also in the generation of danger or costimulatory signals. Enzymes such as aldo-keto reductases (AKR) and glutathione transferases (GST) metabolize prostaglandins and reactive aldehydes with proinflammatory activity, as well as drugs and/or their reactive metabolites. In addition, their metabolic activity can have important consequences for the cellular redox status, and impacts the inflammatory response as well as the balance of inflammatory mediators, which can modulate epigenetic factors and cooperate or interfere with drug-adduct formation. These enzymes are, in turn, targets for covalent modification and regulation by oxidative stress, inflammatory mediators, and drugs. Therefore, they constitute a platform for a complex set of interactions involving drug metabolism, protein haptenation, modulation of the inflammatory response, and/or generation of danger signals with implications in drug hypersensitivity reactions. Moreover, increasing evidence supports their involvement in allergic processes. Here, we will focus on GSTP1-1 and aldose reductase (AKR1B1) and provide a perspective for their involvement in drug hypersensitivity.

Androgens modulate gene expression and specific DNA methylation pattern of steroid 5α-reductases in the frog Silurana tropicalis

In vertebrates, androgens are essential in many biological functions, including reproduction, immune system, metabolism, cardiovascular function, and the central nervous system. The most potent androgen 5α-dihydrotestosterone (5α-DHT), which is actively involved in sexual differentiation and development, is converted from testosterone (T) by the steroid 5α-reductases type 1, 2, and 3 (Srd5α1, Srd5α2, and Srd5α3). Alternatively, steroid 5β-reductase (Srd5β) converts T to 5β-dihydrotestosterone (5β-DHT), a metabolite believed to be involved in steroid clearance. Recent studies suggested that Srd5 isoforms are targets for endocrine disruption. Thus, understanding the regulation of Srd5 is important to expand our knowledge on how exogenous compounds can interfere with these enzymes. In this study, we exposed frog brain, liver, and gonads ex vivo to T, 5α-DHT, and 5β-DHT in order to investigate the regulation of srd5 in response to androgens as a simulation of endocrine disrupting chemicals with androgenic properties. Androgens did not modulate srd5α2, suggesting that this isoform is not regulated by T and 5α-DHT in frogs. However, the DNA methylation of srd5α2 increased following 5α-DHT treatment suggesting that androgens can modulate epigenetic mechanisms in amphibians. In contrast, the DNA methylation of srd5α1 and srd5α3 remained stable after androgen exposure, but the mRNA levels of srd5α1 and srd5α3 were modulated by T, 5α-DHT, and 5β-DHT in a sex- and tissue-specific manner. While T positively regulates srd5α1 and srd5α3 in testes, T negatively regulates srd5α3 in ovaries. Moreover, exposure to T also increased the mRNA level of srd5β in the male brain suggesting a mechanism to protect the brain from androgen action by elimination of T into 5β-DHT. Thus, exogenous compounds with androgenic properties potentially interact with srd5 transcription and DNA methylation pattern, which could adversely affect biological functions of vertebrates during development and reproduction.

Research Resource: A Reference Transcriptome for Constitutive Androstane Receptor and Pregnane X Receptor Xenobiotic Signaling

The pregnane X receptor (PXR) (PXR/NR1I3) and constitutive androstane receptor (CAR) (CAR/NR1I2) members of the nuclear receptor (NR) superfamily of ligand-regulated transcription factors are well-characterized mediators of xenobiotic and endocrine-disrupting chemical signaling. The Nuclear Receptor Signaling Atlas maintains a growing library of transcriptomic datasets involving perturbations of NR signaling pathways, many of which involve perturbations relevant to PXR and CAR xenobiotic signaling. Here, we generated a reference transcriptome based on the frequency of differential expression of genes across 159 experiments compiled from 22 datasets involving perturbations of CAR and PXR signaling pathways. In addition to the anticipated overrepresentation in the reference transcriptome of genes encoding components of the xenobiotic stress response, the ranking of genes involved in carbohydrate metabolism and gonadotropin action sheds mechanistic light on the suspected role of xenobiotics in metabolic syndrome and reproductive disorders. Gene Set Enrichment Analysis showed that although acetaminophen, chlorpromazine, and phenobarbital impacted many similar gene sets, differences in direction of regulation were evident in a variety of processes. Strikingly, gene sets representing genes linked to Parkinson's, Huntington's, and Alzheimer's diseases were enriched in all 3 transcriptomes. The reference xenobiotic transcriptome will be supplemented with additional future datasets to provide the community with a continually updated reference transcriptomic dataset for CAR- and PXR-mediated xenobiotic signaling. Our study demonstrates how aggregating and annotating transcriptomic datasets, and making them available for routine data mining, facilitates research into the mechanisms by which xenobiotics and endocrine-disrupting chemicals subvert conventional NR signaling modalities.

Aldo-keto reductase 1B10 promotes development of cisplatin resistance in gastrointestinal cancer cells through down-regulating peroxisome proliferator-activated receptor-γ-dependent mechanism

Cisplatin (cis-diamminedichloroplatinum, CDDP) is one of the most effective chemotherapeutic drugs that are used for treatment of patients with gastrointestinal cancer cells, but its continuous administration often evokes the development of chemoresistance. In this study, we investigated alterations in antioxidant molecules and functions using a newly established CDDP-resistant variant of gastric cancer MKN45 cells, and found that aldo-keto reductase 1B10 (AKR1B10) is significantly up-regulated with acquisition of the CDDP resistance. In the nonresistant MKN45 cells, the sensitivity to cytotoxic effect of CDDP was decreased and increased by overexpression and silencing of AKR1B10, respectively. In addition, the AKR1B10 overexpression markedly suppressed accumulation and cytotoxicity of 4-hydroxy-2-nonenal that is produced during lipid peroxidation by CDDP treatment, suggesting that the enzyme acts as a crucial factor for facilitation of the CDDP resistance through inhibiting induction of oxidative stress by the drug. Transient exposure to CDDP and induction of the CDDP resistance decreased expression of peroxisome proliferator-activated receptor-γ (PPARγ) in MKN45 and colon cancer LoVo cells. Additionally, overexpression of PPARγ in the cells elevated the sensitivity to the CDDP toxicity, which was further augmented by concomitant treatment with a PPARγ ligand rosiglitazone. Intriguingly, overexpression of AKR1B10 in the cells resulted in a decrease in PPARγ expression, which was recovered by addition of an AKR1B10 inhibitor oleanolic acid, inferring that PPARγ is a downstream target of AKR1B10-dependent mechanism underlying the CDDP resistance. Combined treatment with the AKR1B10 inhibitor and PPARγ ligand elevated the CDDP sensitivity, which was almost the same level as that in the parental cells. These results suggest that combined treatment with the AKR1B10 inhibitor and PPARγ ligand is an effective adjuvant therapy for overcoming CDDP resistance of gastrointestinal cancer cells.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.

Genes of the de novo and Salvage Biosynthesis Pathways of Vitamin B6 are Regulated under Oxidative Stress in the Plant Pathogen Rhizoctonia solani

Vitamin B6 is recognized as an important cofactor required for numerous metabolic enzymes, and has been shown to act as an antioxidant and play a role in stress responses. It can be synthesized through two different routes: salvage and de novo pathways. However, little is known about the possible function of the vitamin B6 pathways in the fungal plant pathogen Rhizoctonia solani. Using genome walking, the de novo biosynthetic pathway genes; RsolPDX1 and RsolPDX2 and the salvage biosynthetic pathway gene, RsolPLR were sequenced. The predicted amino acid sequences of the three genes had high degrees of similarity to other fungal PDX1, PDX2, and PLR proteins and are closely related to other R. solani anastomosis groups. We also examined their regulation when subjected to reactive oxygen species (ROS) stress inducers, the superoxide generator paraquat, or H₂O₂, and compared it to the well-known antioxidant genes, catalase and glutathione-S-transferase (GST). The genes were differentially regulated with transcript levels as high as 33 fold depending on the gene and type of stress reflecting differences in the type of damage induced by ROS. Exogenous addition of the vitamers PN or PLP in culture medium significantly induced the transcription of the vitamin B6 de novo encoding genes as early as 0.5 hour post treatment (HPT). On the other hand, transcription of RsolPLR was vitamer-specific; a down regulation upon supplementation of PN and upregulation with PLP. Our results suggest that accumulation of ROS in R. solani mycelia is linked to transcriptional regulation of the three genes and implicate the vitamin B6 biosynthesis machinery in R. solani, similar to catalases and GST, as an antioxidant stress protector against oxidative stress.

Identification of novel pyrazole–rhodanine hybrid scaffolds as potent inhibitors of aldose reductase: design, synthesis, biological evaluation and molecular docking analysis

A series of novel pyrazole–rhodanine derivatives was designed, synthesized, and biologically evaluated for their potential inhibitory effect on both aldehyde reductase (ALR1) and aldose reductase (ALR2).

Aldo-Keto Reductases 1B in Adrenal Cortex Physiology

Aldose reductase (AKR1B) proteins are monomeric enzymes, belonging to the aldo-keto reductase (AKR) superfamily. They perform oxidoreduction of carbonyl groups from a wide variety of substrates, such as aliphatic and aromatic aldehydes or ketones. Due to the involvement of human aldose reductases in pathologies, such as diabetic complications and cancer, AKR1B subgroup enzymatic properties have been extensively characterized. However, the issue of AKR1B function in non-pathologic conditions remains poorly resolved. Adrenal activities generated large amount of harmful aldehydes from lipid peroxidation and steroidogenesis, including 4-hydroxynonenal (4-HNE) and isocaproaldehyde (4-methylpentanal), which can both be reduced by AKR1B proteins. More recently, some AKR1B isoforms have been shown to be endowed with prostaglandin F synthase (PGFS) activity, suggesting that, in addition to possible scavenger function, they could instigate paracrine signals. Interestingly, the adrenal gland is one of the major sites for human and murine AKR1B expression, suggesting that their detoxifying/signaling activity could be specifically required for the correct handling of adrenal function. Moreover, chronic effects of ACTH result in a coordinated regulation of genes encoding the steroidogenic enzymes and some AKR1B isoforms. This review presents the molecular mechanisms accounting for the adrenal-specific expression of some AKR1B genes. Using data from recent mouse genetic models, we will try to connect their enzymatic properties and regulation with adrenal functions.

Structural Determinants of the Selectivity of 3-Benzyluracil-1-acetic Acids toward Human Enzymes Aldose Reductase and AKR1B10

The human enzymes aldose reductase (AR) and AKR1B10 have been thoroughly explored in terms of their roles in diabetes, inflammatory disorders, and cancer. In this study we identified two new lead compounds, 2-(3-(4-chloro-3-nitrobenzyl)-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)acetic acid (JF0048, 3) and 2-(2,4-dioxo-3-(2,3,4,5-tetrabromo-6-methoxybenzyl)-3,4-dihydropyrimidin-1(2H)-yl)acetic acid (JF0049, 4), which selectively target these enzymes. Although 3 and 4 share the 3-benzyluracil-1-acetic acid scaffold, they have different substituents in their aryl moieties. Inhibition studies along with thermodynamic and structural characterizations of both enzymes revealed that the chloronitrobenzyl moiety of compound 3 can open the AR specificity pocket but not that of the AKR1B10 cognate. In contrast, the larger atoms at the ortho and/or meta positions of compound 4 prevent the AR specificity pocket from opening due to steric hindrance and provide a tighter fit to the AKR1B10 inhibitor binding pocket, probably enhanced by the displacement of a disordered water molecule trapped in a hydrophobic subpocket, creating an enthalpic signature. Furthermore, this selectivity also occurs in the cell, which enables the development of a more efficient drug design strategy: compound 3 prevents sorbitol accumulation in human retinal ARPE-19 cells, whereas 4 stops proliferation in human lung cancer NCI-H460 cells.

A Novel Aldo-Keto Reductase (AKR17A1) of Anabaena sp. PCC 7120 Degrades the Rice Field Herbicide Butachlor and Confers Tolerance to Abiotic Stresses in E. coli

Present study deals with the identification of a novel aldo/keto reductase, AKR17A1 from Anabaena sp. PCC7120 and adds on as 17^th family of AKR superfamily drawn from a wide variety of organisms. AKR17A1 shares many characteristics of a typical AKR such as— (i) conferring tolerance to multiple stresses like heat, UV-B, and cadmium, (ii) excellent activity towards known AKR substrates (isatin and 2-nitrobenzaldehyde), and (iii) obligate dependence on NADPH as a cofactor for enzyme activity. The most novel attribute of AKR17A1, first reported in this study, is its capability to metabolize butachlor, a persistent rice field herbicide that adversely affects agro-ecosystem and non-target organisms. The AKR17A1 catalyzed- degradation of butachlor resulted into formation of 1,2-benzene dicarboxylic acid and 2,6 bis (1,1, dimethylethyl) 4,-methyl phenol as the major products confirmed by GC-MS analysis.

Substrate Specificity, Inhibitor Selectivity and Structure-Function Relationships of Aldo-Keto Reductase 1B15: A Novel Human Retinaldehyde Reductase

Human aldo-keto reductase 1B15 (AKR1B15) is a newly discovered enzyme which shares 92% amino acid sequence identity with AKR1B10. While AKR1B10 is a well characterized enzyme with high retinaldehyde reductase activity, involved in the development of several cancer types, the enzymatic activity and physiological role of AKR1B15 are still poorly known. Here, the purified recombinant enzyme has been subjected to substrate specificity characterization, kinetic analysis and inhibitor screening, combined with structural modeling. AKR1B15 is active towards a variety of carbonyl substrates, including retinoids, with lower kcat and Km values than AKR1B10. In contrast to AKR1B10, which strongly prefers all-trans-retinaldehyde, AKR1B15 exhibits superior catalytic efficiency with 9-cis-retinaldehyde, the best substrate found for this enzyme. With ketone and dicarbonyl substrates, AKR1B15 also shows higher catalytic activity than AKR1B10. Several typical AKR inhibitors do not significantly affect AKR1B15 activity. Amino acid substitutions clustered in loops A and C result in a smaller, more hydrophobic and more rigid active site in AKR1B15 compared with the AKR1B10 pocket, consistent with distinct substrate specificity and narrower inhibitor selectivity for AKR1B15.

Cloning and characterization of a NADH-dependent aldo-keto reductase from a newly isolated Kluyveromyces lactis XP1461

An aldo-keto reductase gene (klakr) from Kluyveromyces lactis XP1461 was cloned and heterologously expressed in Escherichia coli. The aldo-keto reductase KlAKR was purified and found to be NADH-dependent with a molecular weight of approximately 36 kDa. It is active and stable at 30 °C and pH 7.0. The maximal reaction rate (vmax), apparent Michaelis-Menten constant (Km) for NADH and t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate (1a) and catalytic number (kcat) were calculated as 7.63 U mg(-1), 0.204 mM, 4.42 mM and 697.4 min(-1), respectively. Moreover, the KlAKR has broad substrate specificity to a range of aldehydes, ketones and keto-esters, producing chiral alcohol with e.e. or d.e. >99% for the majority of test substrates.

Dual-color immunofluorescent labeling with quantum dots of the diabetes-associated proteins aldose reductase and Toll-like receptor 4 in the kidneys of diabetic rats

Diabetes is one of the major chronic diseases diagnosed worldwide with a common complication of diabetic nephropathy (DN). There are multiple possible mechanisms associated with DN. Aldose reductase (AR) and Toll-like receptor 4 (TLR4) may be involved in the occurrence and development of DN. Here, we describe the distribution of AR and TLR4 in cells and renal tissues of diabetic rats through a quantum dot (QD)-based immunofluorescence technique and conventional immunohistochemistry. As a new type of nanosized fluorophore, QDs have been recognized in imaging applications and have broad prospects in biomedical research. The results of the reported study demonstrate that both the AR and the TLR4 proteins were upregulated in the renal tissues of diabetic rats. Further, to explore the relationship between AR and TLR4 in the pathogenesis of DN, a dual-color immunofluorescent labeling technique based on QDs was applied, where the expressions of AR and TLR4 in the renal tissues of diabetic rats were simultaneously observed – for the first time, as far as we are aware. The optimized QD-based immunofluorescence technique has not only shown a satisfying sensitivity and specificity for the detection of biomarkers in cells and tissues, but also is a valuable supplement of immu-nohistochemistry. The QD-based multiplexed imaging technology provides a new insight into the mechanistic study of the correlation among biological factors as well as having potential applications in the diagnosis and treatment of diseases.

Characterization of hamster NAD+-dependent 3(17)β-hydroxysteroid dehydrogenase belonging to the aldo-keto reductase 1C subfamily

The cDNAs for morphine 6-dehydrogenase (AKR1C34) and its homologous aldo-keto reductase (AKR1C35) were cloned from golden hamster liver, and their enzymatic properties and tissue distribution were compared. AKR1C34 and AKR1C35 similarly oxidized various xenobiotic alicyclic alcohols using NAD(+), but differed in their substrate specificity for hydroxysteroids and inhibitor sensitivity. While AKR1C34 showed 3α/17β/20α-hydroxysteroid dehydrogenase activities, AKR1C35 efficiently oxidized various 3β- and 17β-hydroxysteroids, including biologically active 3β-hydroxy-5α/β-dihydro-C19/C21-steroids, dehydroepiandrosterone and 17β-estradiol. AKR1C35 also differed from AKR1C34 in its high sensitivity to flavonoids, which inhibited competitively with respect to 17β-estradiol (Ki 0.11-0.69 μM). The mRNA for AKR1C35 was expressed liver-specific in male hamsters and ubiquitously in female hamsters, whereas the expression of the mRNA for AKR1C34 displayed opposite sexual dimorphism. Because AKR1C35 is the first 317Β-HYDROXYSTEROID DEHYDROGENASE IN THE AKR SUPERFAMILY: , we also investigated the molecular determinants for the 3β-hydroxysteroid dehydrogenase activity by replacement of Val54 and Cys310 in AKR1C35 with the corresponding residues in AKR1C34, Ala and Phe, respectively. The mutation of Val54Ala, but not Cys310Phe, significantly impaired this activity, suggesting that Val54 plays a critical role in recognition of the steroidal substrate.

Plant aldo-keto reductases (AKRs) as multi-tasking soldiers involved in diverse plant metabolic processes and stress defense: A structure-function update

The aldo-keto reductase (AKR) superfamily comprises of a large number of primarily monomeric protein members, which reduce a broad spectrum of substrates ranging from simple sugars to potentially toxic aldehydes. Plant AKRs can be broadly categorized into four important functional groups, which highlight their roles in diverse plant metabolic reactions including reactive aldehyde detoxification, biosynthesis of osmolytes, secondary metabolism and membrane transport. Further, multiple overlapping functional aspects of plant AKRs including biotic and abiotic stress defense, production of commercially important secondary metabolites, iron acquisition from soil, plant-microbe interactions etc. are discussed as subcategories within respective major groups. Owing to the broad substrate specificity and multiple stress tolerance of the well-characterized AKR4C9 from Arabidopsis thaliana, protein sequences of all the homologues of AKR4C9 (A9-like proteins) from forty different plant species (Phytozome database) were analyzed. The analysis revealed that all A9-like proteins possess strictly conserved key catalytic residues (D-47, Y-52 and K-81) and belong to the pfam00248 and cl00470 AKR superfamilies. Based on structural homology of the three flexible loops of AKR4C9 (Loop A, B and C) responsible for broad substrate specificity, A9-like proteins found in Brassica rapa, Phaseolus vulgaris, Cucumis sativus, Populus trichocarpa and Solanum lycopersicum were predicted to have a similar range of substrate specificity. Thus, plant AKRs can be considered as potential breeding targets for developing stress tolerant varieties in the future. The present review provides a consolidated update on the current research status of plant AKRs with an emphasis on important functional aspects as well as their potential future prospects and an insight into the overall structure-function relationships of A9-like proteins.

Aldose reductases influence prostaglandin F2α levels and adipocyte differentiation in male mouse and human species

Aldose reductases (AKR1B) are widely expressed oxidoreductases whose physiological function remains elusive. Some isoforms are genuine prostaglandin F2α (PGF2α) synthases, suggesting they might influence adipose homeostasis because PGF2α inhibits adipogenesis. This was shown by Akr1b7 gene ablation in the mouse, which resulted in increased adiposity related to a lower PGF2α content in fat. Yet humans have no ortholog gene for Akr1b7, so the role of aldose reductases in human adipose homeostasis remains to be explored. We analyzed expression of genes encoding human and mouse aldose reductase isoforms in adipose tissues and differentiating adipocytes to assess conserved mechanisms regulating PGF2α synthesis and adipogenesis. The Akr1b3 gene encoded the most abundant isoform in mouse adipose tissue, whereas Akr1b7 encoded the only isoform enriched in the stromal vascular fraction. Most mouse aldose reductase gene expression peaked in early adipogenesis of 3T3-L1 cells and diminished with differentiation. In contrast with its mouse ortholog Akr1b3, AKR1B1 expression increased throughout differentiation of human multipotent adipose-derived stem cells, paralleling PGF2α release, whereas PGF2α receptor (FP) levels collapsed in early differentiation. Pharmacological inhibition of aldose reductase using Statil altered PGF2α production and enhanced human multipotent adipose-derived stem adipocyte differentiation. As expected, the adipogenic effects of Statil were counteracted by an FP agonist (cloprostenol). Thus, in both species aldose reductase-dependent PGF2α production could be important in early differentiation to restrict adipogenesis. PGF2α antiadipogenic signaling could then be toned down through the FP receptor or aldose reductases down-regulation in human and mouse cells, respectively. Our data suggest that aldose reductase inhibitors could have obesogenic potential.

Acquisition of doxorubicin resistance facilitates migrating and invasive potentials of gastric cancer MKN45 cells through up-regulating aldo-keto reductase 1B10

Continuous exposure to doxorubicin (DOX) accelerates hyposensitivity to the drug-elicited lethality of gastric cells, with increased risks of the recurrence and serious cardiovascular side effects. However, the detailed mechanisms underlying the reduction of DOX sensitivity remain unclear. In this study, we generated a DOX-resistant variant upon continuously treating human gastric cancer MKN45 cells with incremental concentrations of the drug, and investigated whether the gain of DOX resistance influences gene expression of four aldo-keto reductases (AKRs: 1B10, 1C1, 1C2 and 1C3). RT-PCR analysis revealed that among the enzymes AKR1B10 is most highly up-regulated during the chemoresistance induction. The up-regulation of AKR1B10 was confirmed by analyses of Western blotting and enzyme activity. The DOX sensitivity of MKN45 cells was reduced and elevated by overexpression and inhibition of AKR1B10, respectively. Compared to the parental MKN45 cells, the DOX-resistant cells had higher migrating and invasive abilities, which were significantly suppressed by addition of AKR1B10 inhibitors. Zymographic and real-time PCR analyses also revealed significant increases in secretion and expression of matrix metalloproteinase (MMP) 2 associated with DOX resistance. Moreover, the overexpression of AKR1B10 in the parental cells remarkably facilitated malignant progression (elevation of migrating and invasive potentials) and MMP2 secretion, which were lowered by the AKR1B10 inhibitors. These results suggest that AKR1B10 is a DOX-resistance gene in the gastric cancer cells, and is responsible for elevating the migrating and invasive potentials of the cells through induction of MMP2.

Identification of a determinant for strict NADP(H)-specificity and high sensitivity to mixed-type steroid inhibitor of rabbit aldo-keto reductase 1C33 by site-directed mutagenesis

In rabbit tissues, hydroxysteroid dehydrogenase belonging to the aldo-keto reductase (AKR) superfamily exists in six isoforms (AKRs: 1C5 and 1C29-1C33), sharing >73% amino acid sequence identity. AKR1C33 is strictly NADPH-specific, in contrast to dual NADPH/NADH specificity of the other isoforms. All coenzyme-binding residues of the structurally elucidated AKR1C5 are conserved in other isoforms, except that S217 (interacting with the pyrophosphate moiety) and T273 (interacting with the 2'-phosphate moiety) are replaced with F217 and N272, respectively, in AKR1C33. To explore the determinants for the NADPH specificity of AKR1C33, we prepared its F217S and N272T mutant enzymes. The mutation of F217S, but not N272T, converted AKR1C33 into a dually coenzyme-specific form that showed similar kcat values for NAD(P)H to those of AKR1C32. The reverse mutation (S217F) in dually coenzyme-specific AKR1C32 produced a strictly NADPH-specific form. The F217S mutation also abolished the activity towards 3-keto-5β-cholestanes that are substrates specific to AKR1C33, and markedly decreased the sensitivity to 4-pregnenes (such as deoxycorticosterone and medroxyprogesterone acetate) that were found to be potent mixed-type inhibitors of the wild-type enzyme. The results indicate the important role of F217 in the strict NADPH-dependency, as well as its involvement in the unique catalytic properties of AKR1C33.

Expanding xylose metabolism in yeast for plant cell wall conversion to biofuels

Sustainable biofuel production from renewable biomass will require the efficient and complete use of all abundant sugars in the plant cell wall. Using the cellulolytic fungus Neurospora crassa as a model, we identified a xylodextrin transport and consumption pathway required for its growth on hemicellulose. Reconstitution of this xylodextrin utilization pathway in Saccharomyces cerevisiae revealed that fungal xylose reductases act as xylodextrin reductases, producing xylosyl-xylitol oligomers as metabolic intermediates. These xylosyl-xylitol intermediates are generated by diverse fungi and bacteria, indicating that xylodextrin reduction is widespread in nature. Xylodextrins and xylosyl-xylitol oligomers are then hydrolyzed by two hydrolases to generate intracellular xylose and xylitol. Xylodextrin consumption using a xylodextrin transporter, xylodextrin reductases and tandem intracellular hydrolases in cofermentations with sucrose and glucose greatly expands the capacity of yeast to use plant cell wall-derived sugars and has the potential to increase the efficiency of both first-generation and next-generation biofuel production.

DOI:http://dx.doi.org/10.7554/eLife.05896.001

Plants can be used to make ‘biofuels’, which are more sustainable alternatives to traditional fuels made from petroleum. Unfortunately, most biofuels are currently made from simple sugars or starch extracted from parts of plants that we also use for food, such as the grains of cereal crops.

Making biofuels from the parts of the plant that are not used for food—for example, the stems or leaves—would enable us to avoid a trade-off between food and fuel production. However, most of the sugars in these parts of the plant are locked away in the form of large, complex carbohydrates called cellulose and hemicellulose, which form the rigid cell wall surrounding each plant cell.

Currently, the industrial processes that can be used to make biofuels from plant cell walls are expensive and use a lot of energy. They involve heating or chemically treating the plant material to release the cellulose and hemicellulose. Then, large quantities of enzymes are added to break these carbohydrates down into simple sugars that can then be converted into alcohol (a biofuel) by yeast.

Fungi may be able to provide us with a better solution. Many species are able to grow on plants because they can break down cellulose and hemicellulose into simple sugars they can use for energy. If the genes involved in this process could be identified and inserted into yeast it may provide a new, cheaper method to make biofuels from plant cell walls.

To address this challenge, Li et al. studied how the fungus Neurospora crassa breaks down hemicellulose. This study identified a protein that can transport molecules of xylodextrin—which is found in hemicellulose—into the cells of the fungus, and two enzymes that break down the xylodextrin to make simple sugars, using a previously unknown chemical intermediate. When Li et al. inserted the genes that make the transport protein and the enzymes into yeast, the yeast were able to use plant cell wall material to make simple sugars and convert these to alcohol.

The yeast used more of the xylodextrin when they were grown with an additional source of energy, such as the sugars glucose or sucrose. Li et al.'s findings suggest that giving yeast the ability to break down hemicellulose has the potential to improve the efficiency of biofuel production. The next challenge will be to improve the process so that the yeast can convert the xylodextrin and simple sugars more rapidly.

DOI:http://dx.doi.org/10.7554/eLife.05896.002

CRYPTOCHROME-mediated phototransduction by modulation of the potassium ion channel β-subunit redox sensor

Blue light activation of the photoreceptor CRYPTOCHROME (CRY) evokes rapid depolarization and increased action potential firing in a subset of circadian and arousal neurons in Drosophila melanogaster. Here we show that acute arousal behavioral responses to blue light significantly differ in mutants lacking CRY, as well as mutants with disrupted opsin-based phototransduction. Light-activated CRY couples to membrane depolarization via a well conserved redox sensor of the voltage-gated potassium (K(+)) channel β-subunit (Kvβ) Hyperkinetic (Hk). The neuronal light response is almost completely absent in hk(-/-) mutants, but is functionally rescued by genetically targeted neuronal expression of WT Hk, but not by Hk point mutations that disable Hk redox sensor function. Multiple K(+) channel α-subunits that coassemble with Hk, including Shaker, Ether-a-go-go, and Ether-a-go-go-related gene, are ion conducting channels for CRY/Hk-coupled light response. Light activation of CRY is transduced to membrane depolarization, increased firing rate, and acute behavioral responses by the Kvβ subunit redox sensor.

Using a Label Free Quantitative Proteomics Approach to Identify Changes in Protein Abundance in Multidrug-Resistant Mycobacterium tuberculosis

Reports in recent years indicate that the increasing emergence of resistance to drugs be using to TB treatment. The resistance to them severely affects to options for effective treatment. The emergence of multidrug-resistant tuberculosis has increased interest in understanding the mechanism of drug resistance in M. tuberculosis and the development of new therapeutics, diagnostics and vaccines. In this study, a label-free quantitative proteomics approach has been used to analyze proteome of multidrug-resistant and susceptible clinical isolates of M. tuberculosis and identify differences in protein abundance between the two groups. With this approach, we were able to identify a total of 1,583 proteins. The majority of identified proteins have predicted roles in lipid metabolism, intermediary metabolism, cell wall and cell processes. Comparative analysis revealed that 68 proteins identified by at least two peptides showed significant differences of at least twofolds in relative abundance between two groups. In all protein differences, the increase of some considering proteins such as NADH dehydrogenase, probable aldehyde dehydrogenase, cyclopropane mycolic acid synthase 3, probable arabinosyltransferase A, putative lipoprotein, uncharacterized oxidoreductase and six membrane proteins in resistant isolates might be involved in the drug resistance and to be potential diagnostic protein targets. The decrease in abundance of proteins related to secretion system and immunogenicity (ESAT-6-like proteins, ESX-1 secretion system associated proteins, O-antigen export system and MPT63) in the multidrug-resistant strains can be a defensive mechanism undertaken by the resistant cell.

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.

Synthesis of 8-hydroxy-2-iminochromene derivatives as selective and potent inhibitors of human carbonyl reductase 1

Human carbonyl reductase 1 (CBR1), a member of the short-chain dehydrogenase/reductase superfamily, reduces anthracycline anticancer drugs to their less potent anticancer C-13 hydroxy metabolites, which are linked with pathogenesis of cardiotoxicity, a side effect of the drugs.

Proteomics of muscle chronological ageing in post-menopausal women

Background

Muscle ageing contributes to both loss of functional autonomy and increased morbidity. Muscle atrophy accelerates after 50 years of age, but the mechanisms involved are complex and likely result from the alteration of a variety of interrelated functions. In order to better understand the molecular mechanisms underlying muscle chronological ageing in human, we have undertaken a top-down differential proteomic approach to identify novel biomarkers after the fifth decade of age.

Results

Muscle samples were compared between adult (56 years) and old (78 years) post-menopausal women. In addition to total muscle extracts, low-ionic strength extracts were investigated to remove high abundance myofibrillar proteins and improve the detection of low abundance proteins. Two-dimensional gel electrophoreses with overlapping IPGs were used to improve the separation of muscle proteins. Overall, 1919 protein spots were matched between all individuals, 95 were differentially expressed and identified by mass spectrometry, and they corresponded to 67 different proteins. Our results suggested important modifications in cytosolic, mitochondrial and lipid energy metabolism, which may relate to dysfunctions in old muscle force generation. A fraction of the differentially expressed proteins were linked to the sarcomere and cytoskeleton (myosin light-chains, troponin T, ankyrin repeat domain-containing protein-2, vinculin, four and a half LIM domain protein-3), which may account for alterations in contractile properties. In line with muscle contraction, we also identified proteins related to calcium signal transduction (calsequestrin-1, sarcalumenin, myozenin-1, annexins). Muscle ageing was further characterized by the differential regulation of several proteins implicated in cytoprotection (catalase, peroxiredoxins), ion homeostasis (carbonic anhydrases, selenium-binding protein 1) and detoxification (aldo-keto reductases, aldehyde dehydrogenases). Notably, many of the differentially expressed proteins were central for proteostasis, including heat shock proteins and proteins involved in proteolysis (valosin-containing protein, proteasome subunit beta type-4, mitochondrial elongation factor-Tu).

Conclusions

This study describes the most extensive proteomic analysis of muscle ageing in humans, and identified 34 new potential biomarkers. None of them were previously recognized as differentially expressed in old muscles, and each may represent a novel starting point to elucidate the mechanisms of muscle chronological ageing in humans.

Structural analysis of sulindac as an inhibitor of aldose reductase and AKR1B10

Aldose reductase (AR, AKR1B1) and AKR1B10 are enzymes implicated in important pathologies (diabetes and cancer) and therefore they have been proposed as suitable targets for drug development. Sulindac is the metabolic precursor of the potent non-steroidal anti-inflammatory drug (NSAID) sulindac sulfide, which suppresses prostaglandin production by inhibition of cyclooxygenases (COX). In addition, sulindac has been found to be one of the NSAIDs with higher antitumoral activity, presumably through COX inhibition. However, sulindac anticancer activity could be partially mediated through COX-independent mechanisms, including the participation of AR and AKR1B10. Previously, it had been shown that sulindac and sulindac sulfone were good AR inhibitors and the structure of the ternary complex with NADP(+) and sulindac was described (PDB ID 3U2C). In this work, we determined the three-dimensional structure of AKR1B10 with sulindac and established structure-activity relationships (SAR) of sulindac and their derivatives with AR and AKR1B10. The difference in the IC50 values for sulindac between AR (0.36 μM) and AKR1B10 (2.7 μM) might be explained by the different positioning and stacking interaction given by Phe122/Phe123, and by the presence of two buried and ordered water molecules in AKR1B10 but not in AR. Moreover, SAR analysis shows that the substitution of the sulfinyl group is structurally allowed in sulindac derivatives. Hence, sulindac and its derivatives emerge as lead compounds for the design of more potent and selective AR and AKR1B10 inhibitors.

Biochemical characterization of a functional recombinant aryl-alcohol dehydrogenase from Taiwanofungus camphorata

BACKGROUND

Aryl-alcohol dehydrogenases (AADs) have been known to involve in the metabolism of aromatic compounds.

RESULTS

One TcAAD cDNA (GenBank HQ453361) encoding a putative aryl-alcohol dehydrogenase (AAD) was cloned from Taiwanofungus camphorata. The deduced amino acid sequence is conserved among the reported AADs. A 3-D structural model of the TcAAD has been created based on the known structure of voltage-dependent potassium channels subunit beta-2 (PDB code: 3EAU). To characterize the TcAAD, the coding region was subcloned into an expression vector and transformed into Saccharomyces cerevisiae. The recombinant His6-tagged TcAAD was overexpressed and purified by Ni affinity chromatography. The purified enzyme showed a band of approximately 39 kDa on a 12% SDS-PAGE. The molecular mass determined by MALDI-TOF is 40.58 kDa which suggests that the purified enzyme is a monomeric enzyme. Using veratraldehyde as a substrate, the K_M, V_max of TcADD was determined at pH 6.0. Using benzyl alcohol derivatives as substrates, the oxidizing power of TcADD via NAD⁺ at pH 9.6 was studied.

CONCLUSIONS

The coding sequence of the TcAAD cDNA was introduced into an S. cerevisiae expression system and the active enzyme purified and characterized. Understanding the properties of this TcAAD will be beneficial for its potential in xenobiotic detoxification or production of natural flavors.

The role of cytochromes p450 and aldo-keto reductases in prognosis of breast carcinoma patients

Metabolism of anticancer drugs affects their antitumor effects. This study has investigated the associations of gene expression of enzymes metabolizing anticancer drugs with therapy response and survival of breast carcinoma patients. Gene expression of 13 aldo-keto reductases (AKRs), carbonyl reductase 1, and 10 cytochromes P450 (CYPs) was assessed using quantitative real-time polymerase chain reaction in tumors and paired adjacent nonneoplastic tissues from 68 posttreatment breast carcinoma patients. Eleven candidate genes were then evaluated in an independent series of 50 pretreatment patients. Protein expression of the most significant genes was confirmed by immunoblotting. AKR1A1 was significantly overexpressed and AKR1C1-4, KCNAB1, CYP2C19, CYP3A4, and CYP3A5 downregulated in tumors compared with control nonneoplastic tissues after correction for multiple testing. Significant association of CYP2B6 transcript levels in tumors with expression of hormonal receptors was found in the posttreatment set and replicated in the pretreatment set of patients. Significantly higher intratumoral levels of AKR1C1, AKR1C2, or CYP2W1 were found in responders to neoadjuvant chemotherapy compared with nonresponders. Patients with high AKR7A3 or CYP2B6 levels in the pretreatment set had significantly longer disease-free survival than patients with low levels. Protein products of AKR1C1, AKR1C2, AKR7A3, CYP3A4, and carbonyl reductase (CBR1) were found in tumors and those of AKR1C1, AKR7A3, and CBR1 correlated with their transcript levels. Small interfering RNA-directed knockdown of AKR1C2 or vector-mediated upregulation of CYP3A4 in MDA-MB-231 model cell line had no effect on cell proliferation after paclitaxel treatment in vitro. Prognostic and predictive roles of drug-metabolizing enzymes strikingly differ between posttreatment and pretreatment breast carcinoma patients. Mechanisms of action of AKR1C2, AKR7A3, CYP2B6, CYP3A4, and CBR1 should continue to be further followed in breast carcinoma patients and models.

Functional analysis of insect molting fluid proteins on the protection and regulation of ecdysis

Molting fluid accumulates between the old and new cuticles during periodical ecdysis in Ecdysozoa. Natural defects in insect ecdysis are frequently associated with melanization (an immunity response) occurring primarily in molting fluids, suggesting that molting fluid may impact immunity as well as affect ecdysis. To address this hypothesis, proteomic analysis of molting fluids from Bombyx mori during three different types of ecdysis was performed. Many proteins were newly identified, including immunity-related proteins, in each molting fluid. Molting fluids inhibited the growth of bacteria in vitro. The entomopathogenic fungi Beauveria bassiana, which can escape immune responses in feeding larvae, is quickly recognized by larvae during ecdysis, followed by melanization in molting fluid and old cuticle. Fungal conidia germination was delayed, and no hyphae were detected in the hemocoels of pharate instar insects. Molting fluids protect the delicate pharate instar insects with extremely thin cuticles against microorganisms. To explore the function of molting fluids in ecdysis regulation, based on protein similarity, 32 genes were selected for analysis in ecdysis regulation through RNAi in Tribolium castaneum, a model commonly used to study integument development because RNAi is difficult to achieve in B. mori. We identified 24 molting proteins that affected ecdysis after knockdown, with different physiological functions, including old cuticle protein recycling, molting fluid pressure balance, detoxification, and signal detection and transfer of molting fluids. We report that insects secrete molting fluid for protection and regulation of ecdysis, which indicates a way to develop new pesticides through interrupting insect ecdysis in the future.

High expression of aldo-keto reductase 1B10 is an independent predictor of favorable prognosis in patients with hepatocellular carcinoma

BACKGROUND/AIMS

Upregulation of aldo-keto reductase 1B10 (AKR1B10) through the mitogenic activator protein-1 signaling pathway might promote hepatocarcinogenesis and tumor progression. The goal of this study was to evaluate the prognostic significance of AKR1B10 protein expression in patients with hepatocellular carcinoma after surgery.

METHODS

A tissue microarray was used to detect the expression level of AKR1B10 protein in tumors from 255 patients with hepatocellular carcinoma who underwent curative hepatectomy. The impact of AKR1B10 expression on the survival of patients was analyzed. The median follow-up period was 119.8 months.

RESULTS

High AKR1B10 protein expression was observed in 125 of the 255 patients with hepatocellular carcinoma (49.0%). High AKR1B10 expression was significantly associated with a lack of invasion of the major portal vein (p=0.022), a lack of intrahepatic metastasis (p=0.010), lower the American Joint Committee on Cancer T stage (p=0.016), lower the Barcelona Clinic Liver Cancer stage (p=0.006), and lower α-fetoprotein levels (p=0.020). High AKR1B10 expression was also correlated with a lack of early recurrence (p=0.022). Multivariate analyses of survival revealed that intrahepatic metastases and lower albumin levels were independent predictors of both shorter recurrence-free survival and shorter disease-specific survival. High AKR1B10 expression was an independent predictor of both longer recurrence-free survival (p=0.024) and longer disease-specific survival (p=0.046).

CONCLUSIONS

High AKR1B10 protein expression might be useful as a marker of a favorable prognosis in patients with hepatocellular carcinoma after curative hepatectomy.

Metabolism of gamma hydroxybutyrate in human hepatoma HepG2 cells by the aldo-keto reductase AKR1A1

Gamma hydroxybutyrate (GHB) is a recreational and date-rape drug, for which the detection following ingestion is hampered by rapid metabolism and its endogenous presence. GHB catabolism occurs mainly by its oxidation to succinic semialdehyde (SSA), which converts to succinate and enters the tricarboxylic acid cycle. A high Km aldehyde reductase has previously been reported to catalyse the NADP-dependent oxidation of GHB at high concentrations. It is assumed that this enzyme is identical to the aldo-keto reductase AKR1A1, but its role in GHB oxidation has not been fully evaluated. In this study, the extent of AKR1A1 in GHB metabolism has been determined in HepG2 cells using RNA-interference technology. The gene encoding AKR1A1 was targeted by siRNA. Results demonstrate a successful knock-down of the AKR1A1 gene with 92% reduction in total mRNA and 93% reduction in protein expression. Demolishing AKR1A1 expression in HepG2 cells leads to significant 82% decrease in NADP-dependent GHB-dehydrogenase activity at high concentration (10mM) of GHB. Moreover, when exposing the cells to 50 μM of GHB for 24h, and measuring intracellular and extracellular GHB levels by GC/MS, a significant two-fold increase was observed on GHB intracellular level in silenced cells. In contrast, measuring SSA-reductase activity in silenced cells indicated that AKR1A1 is not involved in endogenous GHB production. These findings describe a pathway for GHB metabolism in the liver which should be useful in GHB exposure cases, and will enable a better understanding of the enzymes participating in its metabolism at natural and overexposed levels.