Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily

Sex hormones reduce NNK detoxification through inhibition of short-chain dehydrogenases/reductases and aldo-keto reductases in vitro

Carbonyl reduction is an important metabolic pathway for endogenous and xenobiotic substances. The tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, nicotine-derived nitrosamine ketone) is classified as carcinogenic to humans (IARC, Group 1) and considered to play the most important role in tobacco-related lung carcinogenesis. Detoxification of NNK through carbonyl reduction is catalyzed by members of the AKR- and the SDR-superfamilies which include AKR1B10, AKR1C1, AKR1C2, AKR1C4, 11β-HSD1 and CBR1. Because some reductases are also involved in steroid metabolism, five different hormones were tested for their inhibitory effect on NNK carbonyl reduction. Two of those hormones were estrogens (estradiol and ethinylestradiol), another two hormones belong to the gestagen group (progesterone and drospirenone) and the last tested hormone was an androgen (testosterone). Furthermore, one of the estrogens (ethinylestradiol) and one of the gestagens (drospirenone) are synthetic hormones, used as hormonal contraceptives. Five of six NNK reducing enzymes (AKR1B10, AKR1C1, AKR1C2, AKR1C4 and 11β-HSD1) were significantly inhibited by the tested sex hormones. Only NNK reduction catalyzed by CBR1 was not significantly impaired. In the case of the other five reductases, gestagens had remarkably stronger inhibitory effects at a concentration of 25 μM (progesterone: 66-88% inhibition; drospirenone: 26-87% inhibition) in comparison to estrogens (estradiol: 17-51% inhibition; ethinylestradiol: 14-79% inhibition) and androgens (14-78% inhibition). Moreover, in most cases the synthetic hormones showed a greater ability to inhibit NNK reduction than the physiologic derivatives. These results demonstrate that male and female sex hormones have different inhibitory potentials, thus indicating that there is a varying detoxification capacity of NNK in men and women which could result in a different risk for developing lung cancer.

Stereospecific Metabolism of R- and S-Warfarin by Human Hepatic Cytosolic Reductases

Coumadin (rac-warfarin) is the most commonly used anticoagulant in the world; however, its clinical use is often challenging because of its narrow therapeutic range and interindividual variations in response. A critical contributor to the uncertainty is variability in warfarin metabolism, which includes mostly oxidative but also reductive pathways. Reduction of each warfarin enantiomer yields two warfarin alcohol isomers, and the corresponding four alcohols retain varying levels of anticoagulant activity. Studies on the kinetics of warfarin reduction have often lacked resolution of parent-drug enantiomers and have suffered from coelution of pairs of alcohol metabolites; thus, those studies have not established the importance of individual stereospecific reductive pathways. We report the first steady-state analysis of R- and S-warfarin reduction in vitro by pooled human liver cytosol. As determined by authentic standards, the major metabolites were 9R,11S-warfarin alcohol for R-warfarin and 9S,11S-warfarin alcohol for S-warfarin. R-warfarin (Vmax 150 pmol/mg per minute, Km 0.67 mM) was reduced more efficiently than S-warfarin (Vmax 27 pmol/mg per minute, Km 1.7 mM). Based on inhibitor phenotyping, carbonyl reductase-1 dominated R-and S-warfarin reduction, followed by aldo-keto reductase-1C3 and then other members of that family. Overall, the carbonyl at position 11 undergoes stereospecific reduction by multiple enzymes to form the S alcohol for both drug enantiomers, yet R-warfarin undergoes reduction preferentially. This knowledge will aid in assessing the relative importance of reductive pathways for R- and S-warfarin and factors influencing levels of pharmacologically active parent drugs and metabolites, thus impacting patient dose responses.

Discovery of Novel and Highly Selective Inhibitors of Calpain for the Treatment of Alzheimer's Disease: 2-(3-Phenyl-1H-pyrazol-1-yl)-nicotinamides

Calpain overactivation has been implicated in a variety of pathological disorders including ischemia/reperfusion injury, cataract formation, and neurodegenerative diseases such as Alzheimer's disease (AD). Herein we describe our efforts leading to the identification of ketoamide-based 2-(3-phenyl-1H-pyrazol-1-yl)nicotinamides as potent and reversible inhibitors of calpain with high selectivity versus related cysteine protease cathepsins, other proteases, and receptors. Broad efficacy in a set of preclinical models relevant to AD suggests that inhibition of calpain represents an attractive approach with potential benefit for the treatment of AD.

Extended Catalytic Scope of a Well-Known Enzyme: Asymmetric Reduction of Iminium Substrates by Glucose Dehydrogenase

NADP(H)-dependent imine reductases (IREDs) are of interest in biocatalytic research due to their ability to generate chiral amines from imine/iminium substrates. In reaction protocols involving IREDs, glucose dehydrogenase (GDH) is generally used to regenerate the expensive cofactor NADPH by oxidation of d-glucose to gluconolactone. We have characterized different IREDs with regard to reduction of a set of bicyclic iminium compounds and have utilized ¹ H NMR and GC analyses to determine degree of substrate conversion and product enantiomeric excess (ee). All IREDs reduced the tested iminium compounds to the corresponding chiral amines. Blank experiments without IREDs also showed substrate conversion, however, thus suggesting an iminium reductase activity of GDH. This unexpected observation was confirmed by additional experiments with GDHs of different origin. The reduction of C=N bonds with good levels of conversion (>50 %) and excellent enantioselectivity (up to >99 % ee) by GDH represents a promiscuous catalytic activity of this enzyme.

Metabolism of F18, a Derivative of Calanolide A, in Human Liver Microsomes and Cytosol

10-Chloromethyl-11-demethyl-12-oxo-calanolide (F18), an analog of calanolide A, is a novel potent nonnucleoside reverse transcriptase inhibitor against HIV-1. Here, we report the metabolic profile and the results of associated biochemical studies of F18 in vitro and in vivo. The metabolites of F18 were identified based on liquid chromatography-electrospray ionization mass spectrometry and/or nuclear magnetic resonance. Twenty-three metabolites of F18 were observed in liver microsomes in vitro. The metabolism of F18 involved 4-propyl chain oxidation, 10-chloromethyl oxidative dechlorination and 12-carbonyl reduction. Three metabolites (M1, M3-1, and M3-2) were also found in rat blood after oral administration of F18 and the reduction metabolites M3-1 and M3-2 were found to exhibit high potency for the inhibition of HIV-1 in vitro. The oxidative metabolism of F18 was mainly catalyzed by cytochrome P450 3A4 in human microsomes, whereas flavin-containing monooxygenases and 11β-hydroxysteroid dehydrogenase were found to be involved in its carbonyl reduction. In human cytosol, multiple carbonyl reductases, including aldo-keto reductase 1C, short-chain dehydrogenases/reductases and quinone oxidoreductase 1, were demonstrated to be responsible for F18 carbonyl reduction. In conclusion, the in vitro metabolism of F18 involves multiple drug metabolizing enzymes, and several metabolites exhibited anti-HIV-1 activities. Notably, the described results provide the first demonstration of the capability of FMOs for carbonyl reduction.

Human carbonyl reductase 1 participating in intestinal first-pass drug metabolism is inhibited by fatty acids and acyl-CoAs

Human carbonyl reductase 1 (CBR1), a member of the short-chain dehydrogenase/reductase (SDR) superfamily, reduces a variety of carbonyl compounds including endogenous isatin, prostaglandin E₂ and 4-oxo-2-nonenal. It is also a major non-cytochrome P450 enzyme in the phase I metabolism of carbonyl-containing drugs, and is highly expressed in the intestine. In this study, we found that long-chain fatty acids and their CoA ester derivatives inhibit CBR1. Among saturated fatty acids, myristic, palmitic and stearic acids were inhibitory, and stearic acid was the most potent (IC₅₀ 9µM). Unsaturated fatty acids (oleic, elaidic, γ-linolenic and docosahexaenoic acids) and acyl-CoAs (palmitoyl-, stearoyl- and oleoyl-CoAs) were more potent inhibitors (IC₅₀ 1.0-2.5µM), and showed high inhibitory selectivity to CBR1 over its isozyme CBR3 and other SDR superfamily enzymes (DCXR and DHRS4) with CBR activity. The inhibition by these fatty acids and acyl-CoAs was competitive with respect to the substrate, showing the K_i values of 0.49-1.2µM. Site-directed mutagenesis of the substrate-binding residues of CBR1 suggested that the interactions between the fatty acyl chain and the enzyme's Met141 and Trp229 are important for the inhibitory selectivity. We also examined CBR1 inhibition by oleic acid in cellular levels: The fatty acid effectively inhibited CBR1-mediated 4-oxo-2-nonenal metabolism in colon cancer DLD1 cells and increased sensitivity to doxorubicin in the drug-resistant gastric cancer MKN45 cells that highly express CBR1. The results suggest a possible new food-drug interaction through inhibition of CBR1-mediated intestinal first-pass drug metabolism by dietary fatty acids.

Nerolidol and Farnesol Inhibit Some Cytochrome P450 Activities but Did Not Affect Other Xenobiotic-Metabolizing Enzymes in Rat and Human Hepatic Subcellular Fractions

Sesquiterpenes, 15-carbon compounds formed from three isoprenoid units, are the main components of plant essential oils. Sesquiterpenes occur in human food, but they are principally taken as components of many folk medicines and dietary supplements. The aim of our study was to test and compare the potential inhibitory effect of acyclic sesquiterpenes, trans-nerolidol, cis-nerolidol and farnesol, on the activities of the main xenobiotic-metabolizing enzymes in rat and human liver in vitro. Rat and human subcellular fractions, relatively specific substrates, corresponding coenzymes and HPLC, spectrophotometric or spectrofluorometric analysis of product formation were used. The results showed significant inhibition of cytochromes P450 (namely CYP1A, CYP2B and CYP3A subfamilies) activities by all tested sesquiterpenes in rat as well as in human hepatic microsomes. On the other hand, all tested sesquiterpenes did not significantly affect the activities of carbonyl-reducing enzymes and conjugation enzymes. The results indicate that acyclic sesquiterpenes might affect CYP1A, CYP2B and CYP3A mediated metabolism of concurrently administered drugs and other xenobiotics. The possible drug-sesquiterpene interactions should be verified in in vivo experiments.

Reductive metabolism of tiaprofenic acid by the human liver and recombinant carbonyl reducing enzymes

Tiaprofenic acid is a widely used anti-inflammatory drug; however, the reductive metabolism of tiaprofenic acid is not yet well understood. Here, we compared the reduction of tiaprofenic acid in microsomes and cytosol from the human liver. The microsomes exhibited lower K_m value toward tiaprofenic acid than the cytosol (K_m = 164 ± 18 μM vs. 569 ± 74 μM, respectively), whereas the cytosol showed higher specific activity during reduction than the microsomes (V_max = 728 ± 52 pmol mg of protein^-1 min^-1 vs. 285 ± 11 pmol mg of protein^-1 min^-1, respectively). Next, a panel of recombinant carbonyl reducing enzymes from AKR and SDR superfamilies has been studied to find the enzymes responsible for the cytosolic reduction of tiaprofenic acid. CBR1 was identified as the reductase of tiaprofenic acid with high specific activity (56,965 ± 6741 pmol mg of protein^-1 min^-1). Three other enzymes, AKR1A1, AKR1B10, and AKR1C4, were also able to reduce tiaprofenic acid, but with very low activity. Thus, CBR1 was shown to be a tiaprofenic acid reductase in vitro and was also suggested to be the principal tiaprofenic acid reductase in vivo.

Human carbonyl reductase 1 as efficient catalyst for the reduction of glutathionylated aldehydes derived from lipid peroxidation

Human recombinant carbonyl reductase 1 (E.C. 1.1.1.184, hCBR1) is shown to efficiently act as aldehyde reductase on glutathionylated alkanals, namely 3-glutathionyl-4-hydroxynonanal (GSHNE), 3-glutathionyl-nonanal, 3-glutathionyl-hexanal and 3-glutathionyl-propanal. The presence of the glutathionyl moiety appears as a necessary requirement for the susceptibility of these compounds to the NADPH-dependent reduction by hCBR1. In fact the corresponding alkanals and alkenals, and the cysteinyl and γ-glutamyl-cysteinyl alkanals adducts were either ineffective or very poorly active as CBR1 substrates. Mass spectrometry analysis reveals the ability of hCBR1 to reduce GSHNE to the corresponding GS-dihydroxynonane (GSDHN) and at the same time to catalyze the oxidation of the hemiacetal form of GSHNE, generating the 3-glutathionylnonanoic-δ-lactone. These data are indicative of the ability of the enzyme to catalyze a disproportion reaction of the substrate through the redox recycle of the pyridine cofactor. A rationale for the observed preferential activity of hCBR1 on different GSHNE diastereoisomers is given by molecular modelling. These results evidence the potential of hCBR1 acting on GSHNE to accomplish a dual role, both in terms of HNE detoxification and, through the production of GSDHN, in terms of involvement into the signalling cascade of the cellular inflammatory response.

Human DHRS7, promising enzyme in metabolism of steroids and retinoids?

The metabolism of steroids and retinoids has been studied in detail for a long time, as these compounds are involved in a broad spectrum of physiological processes. Many enzymes participating in the conversion of such compounds are members of the short-chain dehydrogenase/reductase (SDR) superfamily. Despite great effort, there still remain a number of poorly characterized SDR proteins. According to various bioinformatics predictions, many of these proteins may play a role in the metabolism of steroids and retinoids. Dehydrogenase/reductase (SDR family) member 7 (DHRS7) is one such protein. In a previous study, we determined DHRS7 to be an integral membrane protein of the endoplasmic reticulum facing the lumen which has shown at least in vitro NADPH-dependent reducing activity toward several eobiotics and xenobiotics bearing a carbonyl moiety. In the present paper pure DHRS7 was used for a more detailed study of both substrate screening and an analysis of kinetics parameters of the physiologically important substrates androstene-3,17-dione, cortisone and all-trans-retinal. Expression patterns of DHRS7 at the mRNA as well as protein level were determined in a panel of various human tissue samples, a procedure that has enabled the first estimation of the possible biological function of this enzyme. DHRS7 is expressed in tissues such as prostate, adrenal glands, liver or intestine, where its activity could be well exploited. Preliminary indications show that DHRS7 exhibits dual substrate specificity recognizing not only steroids but also retinoids as potential substrates and could be important in the metabolism of these signalling molecules.

Characterization of the Canine Anthracycline-Metabolizing Enzyme Carbonyl Reductase 1 (cbr1) and the Functional Isoform cbr1 V218

The anthracyclines doxorubicin and daunorubicin are used in the treatment of various human and canine cancers, but anthracycline-related cardiotoxicity limits their clinical utility. The formation of anthracycline C-13 alcohol metabolites (e.g., doxorubicinol and daunorubicinol) contributes to the development of anthracycline-related cardiotoxicity. The enzymes responsible for the synthesis of anthracycline C-13 alcohol metabolites in canines remain to be elucidated. We hypothesized that canine carbonyl reductase 1 (cbr1), the homolog of the prominent anthracycline reductase human CBR1, would have anthracycline reductase activity. Recombinant canine cbr1 (molecular weight: 32.8 kDa) was purified from Escherichia coli. The enzyme kinetics of "wild-type" canine cbr1 (cbr1 D218) and a variant isoform (cbr1 V218) were characterized with the substrates daunorubicin and menadione, as well as the flavonoid inhibitor rutin. Canine cbr1 catalyzes the reduction of daunorubicin to daunorubicinol, with cbr1 D218 and cbr1 V218 displaying different kinetic parameters (cbr1 D218 Km: 188 ± 144 μM versus cbr1 V218 Km: 527 ± 136 μM, P < 0.05, and cbr1 D218 Vmax: 6446 ± 3615 nmol/min per milligram versus cbr1 V218 Vmax: 15539 ± 2623 nmol/min per milligram, P < 0.01). Canine cbr1 also metabolized menadione (cbr1 D218 Km: 104 ± 50 μM, Vmax: 2034 ± 307 nmol/min per milligram). Rutin acted as a competitive inhibitor for the reduction of daunorubicin (cbr1 D218 Ki: 1.84 ± 1.02 μM, cbr1 V218 Ki: 1.38 ± 0.47 μM). These studies show that canine cbr1 metabolizes daunorubicin and provide the necessary foundation to characterize the role of cbr1 in the variable pharmacodynamics of anthracyclines in canine cancer patients.

11β-Hydroxysteroid dehydrogenase 1: Regeneration of active glucocorticoids is only part of the story

11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1) is an endoplasmic reticulum membrane enzyme with its catalytic site facing the luminal space. It functions primarily as a reductase, driven by the supply of its cosubstrate NADPH by hexose-6-phosphate dehydrogenase (H6PDH). Extensive research has been performed on the role of 11β-HSD1 in the regeneration of active glucocorticoids and its role in inflammation and metabolic disease. Besides its important role in the fine-tuning of glucocorticoid action, 11β-HSD1 is a multi-functional carbonyl reductase converting several 11- and 7-oxosterols into the respective 7-hydroxylated forms. Moreover, 11β-HSD1 has a role in phase I biotransformation reactions and catalyzes the carbonyl reduction of several non-steroidal xenobiotics. Recent observations from experiments using selective inhibitors and studies with transgenic mice indicated a role for 11β-HSD1 in oxysterol metabolism and in bile acid homeostasis, with evidence for glucocorticoid-independent effects on gene expression. This review focuses on the promiscuity of 11β-HSD1 to accept structurally distinct substrates and discusses recent progress mainly on non-glucocorticoid substrates. This article is part of a Special Issue entitled 'Enzyme Promiscuity and Diversity'.

NADP(+)-dependent dehydrogenase activity of carbonyl reductase on glutathionylhydroxynonanal as a new pathway for hydroxynonenal detoxification

An NADP(+)-dependent dehydrogenase activity on 3-glutathionyl-4-hydroxynonanal (GSHNE) was purified to electrophoretic homogeneity from a line of human astrocytoma cells (ADF). Proteomic analysis identified this enzymatic activity as associated with carbonyl reductase 1 (EC 1.1.1.184). The enzyme is highly efficient at catalyzing the oxidation of GSHNE (KM 33 µM, kcat 405 min(-1)), as it is practically inactive toward trans-4-hydroxy-2-nonenal (HNE) and other HNE-adducted thiol-containing amino acid derivatives. Combined mass spectrometry and nuclear magnetic resonance spectroscopy analysis of the reaction products revealed that carbonyl reductase oxidizes the hydroxyl group of GSHNE in its hemiacetal form, with the formation of the corresponding 3-glutathionylnonanoic-δ-lactone. The relevance of this new reaction catalyzed by carbonyl reductase 1 is discussed in terms of HNE detoxification and the recovery of reducing power.

Pharmacokinetic interactions of breast cancer chemotherapeutics with human doxorubicin reductases

Paclitaxel (PTX), docetaxel (DTX), 5-fluorouracil (5-FU), cyclophosphamide (CYC) or tamoxifen (TMX) are combined with doxorubicin (DOX) in first-line chemotherapy regimens that are indicated for breast cancer patients. Although the efficacies of these drugs in combination treatments have been demonstrated in clinical practice, their possible interference with DOX metabolism has not been described in detail to date. In the present study, we investigated the possible interactions of human carbonyl reducing enzymes with 5-FU, PTX, DTX, CYC and TMX. First, the reducing activities of carbonyl reducing enzymes toward DOX were tested using incubations with purified recombinant enzymes. In the subsequent studies, we investigated the possible effects of the tested anticancer agents on the DOX-reducing activities of the most potent enzymes (AKR1C3, CBR1 and AKR1A1) and on the DOX metabolism driven by MCF7, HepG2 and human liver cytosols. In both of these assays, we observed that CYC and its active metabolites inhibited DOX metabolism. In the final study, we tracked the changes in AKR1C3, CBR1 and AKR1A1 expression levels following exposure to the tested cytostatics in MCF7 and HepG2 cells. Consequently, no significant changes in the expression levels of tested enzymes were detected in either cell line. Based on these findings, it is feasible to presume that inhibition rather than induction plays a role in the interactions of the tested anticancer agents with DOX-reducing enzymes. In conclusion, our results describe important molecular events that occur during combination breast cancer therapies and might modulate pharmacokinetic DOX resistance and/or behaviour.

RNA sequencing identifies upregulated kyphoscoliosis peptidase and phosphatidic acid signaling pathways in muscle hypertrophy generated by transgenic expression of myostatin propeptide

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, plays a crucial negative role in muscle growth. MSTN mutations or inhibitions can dramatically increase muscle mass in most mammal species. Previously, we generated a transgenic mouse model of muscle hypertrophy via the transgenic expression of the MSTN N-terminal propeptide cDNA under the control of the skeletal muscle-specific MLC1 promoter. Here, we compare the mRNA profiles between transgenic mice and wild-type littermate controls with a high-throughput RNA sequencing method. The results show that 132 genes were significantly differentially expressed between transgenic mice and wild-type control mice; 97 of these genes were up-regulated, and 35 genes were down-regulated in the skeletal muscle. Several genes that had not been reported to be involved in muscle hypertrophy were identified, including up-regulated myosin binding protein H (mybph), and zinc metallopeptidase STE24 (Zmpste24). In addition, kyphoscoliosis peptidase (Ky), which plays a vital role in muscle growth, was also up-regulated in the transgenic mice. Interestingly, a pathway analysis based on grouping the differentially expressed genes uncovered that cardiomyopathy-related pathways and phosphatidic acid (PA) pathways (Dgki, Dgkz, Plcd4) were up-regulated. Increased PA signaling may increase mTOR signaling, resulting in skeletal muscle growth. The findings of the RNA sequencing analysis help to understand the molecular mechanisms of muscle hypertrophy caused by MSTN inhibition.

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.

Aldo-keto reductase 1C3 (AKR1C3) is associated with the doxorubicin resistance in human breast cancer via PTEN loss

Aldo-keto reductase 1C3 (AKR1C3), one member of the aldo-keto reductase superfamily, is involved in a variety of cancers. Recently, AKR1C3 has been demonstrated to be related with the doxorubicin (DOX) resistance in human breast cancer. Here, we attempted to explore the resistance mechanism mediated by AKR1C3. First, one DOX resistant breast cancer cell line MCF-7/DOX was successfully established and an increased level of AKR1C3 was observed in the MCF-7/DOX cells compared to the parental MCF-7 cells. To investigate the contribution of AKR1C3 in the DOX resistance, we further established an AKR1C3 overexpression cell line, referred to MCF-7/AKR1C3. In the MCF-7/AKR1C3 cells, the DOX induced cytotoxicity, detected by CCK-8 cell viability assay and DAPI staining, was greatly reduced (3.2-fold increase in the IC50 value). Interestingly, a loss of tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) was observed when AKR1C3 was overexpressed. Secondary to the PTEN loss, the activated Akt also markedly increased. In addition, the AKR1C3 mediated DOX resistance can be conquered by the Akt inhibitor (LY294002). Furthermore, we found that the expression levels of AKR1C3 and PTEN had a negative relationship in the human breast tumor tissues (the standard correlation coefficient=-0.71; P=0.048). In conclusion, our data suggested that the AKR1C3 mediated DOX resistance might be resulted from the activation of anti-apoptosis PTEN/Akt pathway via PTEN loss. AKR1C3 may present a potential therapeutic target in addressing DOX resistance in breast cancer.

Curcumin is a tight-binding inhibitor of the most efficient human daunorubicin reductase--Carbonyl reductase 1

Curcumin is a major component of the plant Curcuma longa L. It is traditionally used as a spice and coloring in foods and is an important ingredient in curry. Curcuminoids have anti-oxidant and anti-inflammatory properties and gained increasing attention as potential neuroprotective and cancer preventive compounds. In the present study, we report that curcumin is a potent tight-binding inhibitor of human carbonyl reductase 1 (CBR1, Ki=223 nM). Curcumin acts as a non-competitive inhibitor with respect to the substrate 2,3-hexandione as revealed by plotting IC50-values against various substrate concentrations and most likely as a competitive inhibitor with respect to NADPH. Molecular modeling supports the finding that curcumin occupies the cofactor binding site of CBR1. Interestingly, CBR1 is one of the most effective human reductases in converting the anthracycline anti-tumor drug daunorubicin to daunorubicinol. The secondary alcohol metabolite daunorubicinol has significantly reduced anti-tumor activity and shows increased cardiotoxicity, thereby limiting the clinical use of daunorubicin. Thus, inhibition of CBR1 may increase the efficacy of daunorubicin in cancer tissue and simultaneously decrease its cardiotoxicity. Western-blots demonstrated basal expression of CBR1 in several cell lines. Significantly less daunorubicin reduction was detected after incubating A549 cell lysates with increasing concentrations of curcumin (up to 60% less with 50 μM curcumin), suggesting a beneficial effect in the co-treatment of anthracycline anti-tumor drugs together with curcumin.

Towards a systematic analysis of human short-chain dehydrogenases/reductases (SDR): Ligand identification and structure-activity relationships

Short-chain dehydrogenases/reductases (SDRs) constitute a large, functionally diverse branch of enzymes within the class of NAD(P)(H) dependent oxidoreductases. In humans, over 80 genes have been identified with distinct metabolic roles in carbohydrate, amino acid, lipid, retinoid and steroid hormone metabolism, frequently associated with inherited genetic defects. Besides metabolic functions, a subset of atypical SDR proteins appears to play critical roles in adapting to redox status or RNA processing, and thereby controlling metabolic pathways. Here we present an update on the human SDR superfamily and a ligand identification strategy using differential scanning fluorimetry (DSF) with a focused library of oxidoreductase and metabolic ligands to identify substrate classes and inhibitor chemotypes. This method is applicable to investigate structure-activity relationships of oxidoreductases and ultimately to better understand their physiological roles.

Structure-based conversion of the coenzyme requirement of a short-chain dehydrogenase/reductase involved in bacterial alginate metabolism

The alginate-assimilating bacterium, Sphingomonas sp. strain A1, degrades the polysaccharides to monosaccharides through four alginate lyase reactions. The resultant monosaccharide, which is nonenzymatically converted to 4-deoxy-L-erythro-5-hexoseulose uronate (DEH), is further metabolized to 2-keto-3-deoxy-D-gluconate by NADPH-dependent reductase A1-R in the short-chain dehydrogenase/reductase (SDR) family. A1-R-deficient cells produced another DEH reductase, designated A1-R', with a preference for NADH. Here, we show the identification of a novel NADH-dependent DEH reductase A1-R' in strain A1, structural determination of A1-R' by x-ray crystallography, and structure-based conversion of a coenzyme requirement in SDR enzymes, A1-R and A1-R'. A1-R' was purified from strain A1 cells and enzymatically characterized. Except for the coenzyme requirement, there was no significant difference in enzyme characteristics between A1-R and A1-R'. Crystal structures of A1-R' and A1-R'·NAD(+) complex were determined at 1.8 and 2.7 Å resolutions, respectively. Because of a 64% sequence identity, overall structures of A1-R' and A1-R were similar, although a difference in the coenzyme-binding site (particularly the nucleoside ribose 2' region) was observed. Distinct from A1-R, A1-R' included a negatively charged, shallower binding site. These differences were caused by amino acid residues on the two loops around the site. The A1-R' mutant with the two A1-R-typed loops maintained potent enzyme activity with specificity for NADPH rather than NADH, demonstrating that the two loops determine the coenzyme requirement, and loop exchange is a promising method for conversion of coenzyme requirement in the SDR family.

Structure of a short-chain dehydrogenase/reductase (SDR) within a genomic island from a clinical strain of Acinetobacter baumannii

Over 15% of the genome of an Australian clinical isolate of Acinetobacter baumannii occurs within genomic islands. An uncharacterized protein encoded within one island feature common to this and other International Clone II strains has been studied by X-ray crystallography. The 2.4 Å resolution structure of SDR-WM99c reveals it to be a new member of the classical short-chain dehydrogenase/reductase (SDR) superfamily. The enzyme contains a nucleotide-binding domain and, like many other SDRs, is tetrameric in form. The active site contains a catalytic tetrad (Asn117, Ser146, Tyr159 and Lys163) and water molecules occupying the presumed NADP cofactor-binding pocket. An adjacent cleft is capped by a relatively mobile helical subdomain, which is well positioned to control substrate access.

The mechanism of enterohepatic circulation in the formation of gallstone disease

Bile acids entering into enterohepatic circulating are primary acids synthesized from cholesterol in hepatocyte. They are secreted actively across canalicular membrane and carried in bile to gallbladder, where they are concentrated during digestion. About 95 % BAs are actively taken up from the lumen of terminal ileum efficiently, leaving only approximately 5 % (or approximately 0.5 g/d) in colon, and a fraction of bile acids are passively reabsorbed after a series of modifications in the human large intestine including deconjugation and oxidation of hydroxy groups. Bile salts hydrolysis and hydroxy group dehydrogenation reactions are performed by a broad spectrum of intestinal anaerobic bacteria. Next, hepatocyte reabsorbs bile acids from sinusoidal blood, which are carried to liver through portal vein via a series of transporters. Bile acids (BAs) transporters are critical for maintenance of the enterohepatic BAs circulation, where BAs exert their multiple physiological functions including stimulation of bile flow, intestinal absorption of lipophilic nutrients, solubilization, and excretion of cholesterol. Tight regulation of BA transporters via nuclear receptors (NRs) is necessary to maintain proper BA homeostasis. In conclusion, disturbances of enterohepatic circulation may account for pathogenesis of gallstones diseases, including BAs transporters and their regulatory NRs and the metabolism of intestinal bacterias, etc.

Cloning and characterization of four rabbit aldo-keto reductases featuring broad substrate specificity for xenobiotic and endogenous carbonyl compounds: relationship with multiple forms of drug ketone reductases

Multiple forms of reductases for several drug ketones were isolated from rabbit liver, but their interrelationship and physiologic roles remain unknown. We isolated cDNAs for four aldo-keto reductases (AKR1C30, AKR1C31, AKR1C32, and AKR1C33), which share high amino acid sequence identity with the partial sequences of two rabbit naloxone reductases. The four recombinant enzymes reduced a variety of carbonyl compounds, including endogenous α-dicarbonyls (e.g., isatin and diacetyl), aldehydes (e.g., farnesal and 4-oxo-2-nonenal), and ketosteroids. They differed in specificity for drug ketones and ketosteroids. Although daunorubicin and befunolol were common substrates of all of the enzymes, AKR enzymes specifically reduced naloxone (AKR1C30, AKR1C32, and AKR1C33), metyrapone (AKR1C32 and AKR1C33), loxoprofen (AKR1C31 and AKR1C32), ketotifen (AKR1C30), and naltrexone and fenofibric acid (AKR1C33). AKR1C30 reduced only 17-keto-5β-androstanes, whereas the other enzymes were active toward 3-, 17-, and 20-ketosteroids, and AKR1C33 further reduced 3-keto groups of bile acids and 7α-hydroxy-5β-cholestanes. In addition, AKR1C30, AKR1C31, AKR1C32, and AKR1C33 were selectively inhibited by carbenoxolone, baccharin, phenolphthalein, and zearalenone, respectively. The mRNAs for the four enzymes were ubiquitously expressed in male rabbit tissues, in which highly expressed tissues were the brain, heart, liver, kidney, intestine, colon, and testis (for AKR1C30 and AKR1C31); brain, heart, liver, kidney, testis, lung, and adrenal gland (for AKR1C32); and liver and intestine (for AKR1C33). Thus, the four enzymes correspond to the multiple drug ketone reductases, and may function in the metabolisms of steroids, isatin and reactive carbonyl compounds, and bile acid synthesis.

Identification and stress-induced expression of three 3β-hydroxysteroid dehydrogenases from Erysimum crepidifolium Rchb. and their putative role in cardenolide biosynthesis

3β-Hydroxysteroid dehydrogenases (3βHSD) are supposed to be involved in cardenolide biosynthesis in plants. Erysimum crepidifolium Rchb., a member of the Brassicaceae accumulating cardenolides, is a close relative to Arabidopsis thaliana. Full length cDNAs encoding for three individual 3βHSDs (EcHSD1, EcHSD2, EcHSD3) were isolated from E. crepidifolium leaves. EcHSD1 and EcHSD2 encode proteins assembled from 257 amino acids whereas EcHSD3 encodes a protein assembled from 260 amino acids. All three proteins qualify as members of the short-chain dehydrogenases/reductases family of proteins (SDRs). EcHSD1 and EcHSD2 shared a high amino acid sequence identity of about 86% and 91% with putative 3βHSDs of A. thaliana (AT2G47140 and AT2G47130). EcHSD3 showed high homology to the A. thaliana SDRs AT2G47150 (74%) and AT2G47120 (81%). All three EcHSD genes were expressed in Escherichia coli and the recombinant enzymes were characterized biochemically. All three recombinant EcHSDs catalyzed the dehydrogenation of pregnenolone and the 3-reduction of 5α/β-pregnane-3,20-dione when NAD and NADH were used as cosubstrates, respectively. After exposure to different stress conditions, no increased transcription was seen for EcHSD1 whereas EcHSD2 was expressed four times higher under osmotic stress than under control conditions. EcHSD3 expression was 10 times and 6 times higher after osmotic stress and MeJA treatment, respectively, than in controls.

Interindividual variability in the cardiac expression of anthracycline reductases in donors with and without Down syndrome

PURPOSE

The intracardiac synthesis of anthracycline alcohol metabolites (e.g., daunorubicinol) contributes to the pathogenesis of anthracycline-related cardiotoxicity. Cancer patients with Down syndrome (DS) are at increased risk for anthracycline-related cardiotoxicity. We profiled the expression of anthracycline metabolizing enzymes in hearts from donors with- and without- DS.

METHODS

Cardiac expression of CBR1, CBR3, AKR1A1, AKR1C3 and AKR7A2 was examined by quantitative real time PCR, quantitative immunoblotting, and enzyme activity assays using daunorubicin. The CBR1 polymorphism rs9024 was investigated by allelic discrimination with fluorescent probes. The contribution of CBRs/AKRs proteins to daunorubicin reductase activity was examined by multiple linear regression.

RESULTS

CBR1 was the most abundant transcript (average relative expression; DS: 81%, non-DS: 58%), and AKR7A2 was the most abundant protein (average relative expression; DS: 38%, non-DS: 35%). Positive associations between cardiac CBR1 protein levels and daunorubicin reductase activity were found for samples from donors with- and without- DS. Regression analysis suggests that sex, CBR1, AKR1A1, and AKR7A2 protein levels were significant contributors to cardiac daunorubicin reductase activity. CBR1 rs9024 genotype status impacts on cardiac CBR1 expression in non-DS hearts.

CONCLUSIONS

CBR1, AKR1A1, and AKR7A2 protein levels point to be important determinants for predicting the synthesis of cardiotoxic daunorubicinol in heart.

Structural functionality, catalytic mechanism modeling and molecular allergenicity of phenylcoumaran benzylic ether reductase, an olive pollen (Ole e 12) allergen

Isoflavone reductase-like proteins (IRLs) are enzymes with key roles in the metabolism of diverse flavonoids. Last identified olive pollen allergen (Ole e 12) is an IRL relevant for allergy amelioration, since it exhibits high prevalence among atopic patients. The goals of this study are the characterization of (A) the structural-functionality of Ole e 12 with a focus in its catalytic mechanism, and (B) its molecular allergenicity by extensive analysis using different molecular computer-aided approaches covering (1) physicochemical properties and functional-regulatory motifs, (2) sequence analysis, 2-D and 3D structural homology modeling comparative study and molecular docking, (3) conservational and evolutionary analysis, (4) catalytic mechanism modeling, and (5) sequence, structure-docking based B-cell epitopes prediction, while T-cell epitopes were predicted by inhibitory concentration and binding score methods. Structural-based detailed features, phylogenetic and sequences analysis have identified Ole e 12 as phenylcoumaran benzylic ether reductase. A catalytic mechanism has been proposed for Ole e 12 which display Lys133 as one of the conserved residues of the IRLs catalytic tetrad (Asn-Ser-Tyr-Lys). Structure characterization revealed a conserved protein folding among plants IRLs. However, sequence polymorphism significantly affected residues involved in the catalytic pocket structure and environment (cofactor and substrate interaction-recognition). It might also be responsible for IRLs isoforms functionality and regulation, since micro-heterogeneities affected physicochemical and posttranslational motifs. This polymorphism might have large implications for molecular differences in B- and T-cells epitopes of Ole e 12, and its identification may help designing strategies to improve the component-resolving diagnosis and immunotherapy of pollen and food allergy through development of molecular tools.

Characterization of a newly synthesized carbonyl reductase and construction of a biocatalytic process for the synthesis of ethyl (S)-4-chloro-3-hydroxybutanoate with high space-time yield

A carbonyl reductase (SCR2) gene was synthesized and expressed in Escherichia coli after codon optimization to investigate its biochemical properties and application in biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE), which is an important chiral synthon for the side chain of cholesterol-lowering drug. The recombinant SCR2 was purified and characterized using ethyl 4-chloro-3-oxobutanoate (COBE) as substrate. The specific activity of purified enzyme was 11.9 U mg(-1). The optimum temperature and pH for enzyme activity were 45 °C and pH 6.0, respectively. The half-lives of recombinant SCR2 were 16.5, 7.7, 2.2, 0.41, and 0.05 h at 30 °C, 35 °C, 40 °C, 45 °C, and 50 °C, respectively, and it was highly stable in acidic environment. This SCR2 displayed a relatively narrow substrate specificity. The apparent K m and V max values of purified enzyme for COBE are 6.4 mM and 63.3 μmol min(-1) mg(-1), respectively. The biocatalytic process for the synthesis of (S)-CHBE was constructed by this SCR2 in an aqueous-organic solvent system with a substrate fed-batch strategy. At the final COBE concentration of 1 M, (S)-CHBE with yield of 95.3% and e.e. of 99% was obtained after 6-h reaction. In this process, the space-time yield per gram of biomass (dry cell weight, DCW) and turnover number of NADP(+) to (S)-CHBE were 26.5 mmol L(-1) h(-1) g(-1) DCW and 40,000 mol/mol, respectively, which were the highest values as compared with other works.

Comparative inhibition of tetrameric carbonyl reductase activity in pig heart cytosol by alkyl 4-pyridyl ketones

CONTEXT AND OBJECTIVE

The present study is to elucidate the comparative inhibition of tetrameric carbonyl reductase (TCBR) activity by alkyl 4-pyridyl ketones, and to characterize its substrate-binding domain.

MATERIALS AND METHODS

The inhibitory effects of alkyl 4-pyridyl ketones on the stereoselective reduction of 4-benzoylpyridine (4-BP) catalyzed by TCBR were examined in the cytosolic fraction of pig heart.

RESULTS

Of alkyl 4-pyridyl ketones, 4-hexanoylpyridine, which has a straight-chain alkyl group of five carbon atoms, inhibited most potently TCBR activity and was a competitive inhibitor. Furthermore, cyclohexyl pentyl ketone, which is substituted by cyclohexyl group instead of phenyl group of hexanophenone, had much lower ability to be reduced than hexanophenone.

DISCUSSION AND CONCLUSION

These results suggest that in addition to a hydrophobic cleft corresponding to a straight-chain alkyl group of five carbon atoms, a hydrophobic pocket with affinity for an aromatic group is located in the substrate-binding domain of TCBR.

SDR9C7 promotes lymph node metastases in patients with esophageal squamous cell carcinoma

Background

The major reason for the poor prognosis of esophageal squamous cell carcinoma (ESCC) patients is lymph node (LN) metastases.

Methodology/Principal

In the present study, gene expression profiling assay (GEP) was performed to identify the differences in gene expression profiles between primary ESCC tumors that were with LN metastases (N₊) and those without LN metastases (N_-).

Conclusions/Significance

A total of 23 genes were identified as being significantly elevated, and 30 genes were sharply decreased in ESCC tumors that were N₊ compared with N- tumors. Among these genes, two transcripts of the short chain dehydrogenase/reductase family 9C, member 7 (SDR9C7) were observed 7 times more frequently in N₊ compared with N_- tumors. Immunohistochemical staining showed that SDR9C7 expression closely correlated with metastasis, and would be a prognostic marker for ESCC patients. To investigate the role of SDR9C7 in the ESCC metastasis, repeated transwell assays were adopted to establish highly and non-invasive ESCC sublines, and western blot showed that SDR9C7 expression was markedly higher in highly invasive cells compared with non-invasive ones. Down-regulation of SDR9C7 dramatically inhibited the metastatic abilities in vitro and in vivo, and repressed the expression of MMP11 in highly invasive cells, indicating that SDR9C7 promotes ESCC metastasis partly through regulation of MMP11, and might be a potential prognostic and therapeutic marker for ESCC patients.

Regulation of human carbonyl reductase 1 (CBR1, SDR21C1) gene by transcription factor Nrf2

Monomeric carbonyl reductase 1 (CBR1, SDR21C1) is a member of the short-chain dehydrogenase/reductase superfamily and is involved in the metabolism of anthracycline anti-cancer drugs, prostaglandins, and isatin, which is an endogenous inhibitor of monoamine oxidases. Additionally, cancer progression may be partly regulated by CBR1. In the present study, we screened more than 10 drugs for the induction of the human CBR1 gene to investigate its regulation. Of the drugs, butylated hydroxyanisole (BHA) was found to be an inducer. BHA induced the mRNA and protein expression of CBR1 in hepatoma HepG2 cells. In a luciferase reporter gene assay, the promoter region between -2062 bp and the transcription start site of CBR1 was also activated by BHA. The transcription factor Nrf2 is known to be activated by BHA. There are 2 anti-oxidant responsive elements (ARE) that are bound by Nrf2 in this region. Mutation analyses revealed that one of the AREs participates in the gene regulation of CBR1 by Nrf2. Electrophoretic mobility shift assay revealed that Nrf2 binds the site. Moreover, to determine whether the functional ARE of CBR1 is conserved with the promoter region of homologues in other species, the nucleotide sequences of the functional AREs of the Chcr1 and Chcr2 genes, which are the Chinese hamster homologues of CBR1, were determined. The region has 2 AREs, and these genes were also induced by the forced expression of Nrf2 (cotransfection of pNrf2) in the luciferase reporter gene assay. In conclusion, Nrf2 is a novel transcriptional regulator of CBR1 genes in humans and the Chinese hamster. Because the regulation of CBR1 appears to be important for diseases, the induction of CBR1 by Nrf2 may be a therapeutic target.

MicroRNAs differentially regulate carbonyl reductase 1 (CBR1) gene expression dependent on the allele status of the common polymorphic variant rs9024

MicroRNAs (miRNAs) are small RNAs responsible for the post-transcriptional regulation of a variety of human genes. To date, their involvement in the regulation of CBR1 is unknown. This study reports for the first time the identification of microRNA-574-5p (hsa-miR-574-5p) and microRNA-921 (hsa-miR-921) as two miRNAs capable of interacting with the 3'-untranslated region (3'-UTR) of the CBR1 gene and downregulating CBR1 expression. Furthermore, we demonstrate that a common single-nucleotide polymorphism (SNP) in the CBR1 3'-UTR (rs9024, CBR1 1096G>A) differentially impacts the regulation of CBR1 by hsa-miR-574-5p and hsa-miR-921 dependent on genotype. First, four candidate miRNAs were selected based on bioinformatic analyses, and were tested in Chinese hamster ovary (CHO) cells transfected with CBR1 3'-UTR constructs harboring either the G or A allele for rs9024. We found that hsa-miR-574-5p and hsa-miR-921 significantly decreased luciferase activity in CHO cells transfected with the CBR1 3'-UTR construct carrying the major rs9024 G allele by 35% and 46%, respectively. The influence of these miRNAs was different in cells transfected with a CBR1 3'-UTR construct containing the minor rs9024 A allele in that only hsa-miR-574-5p had a demonstrable effect (i.e., 52% decrease in lucifersase activity). To further determine the functional effects of miRNA-mediated regulation of polymorphic CBR1, we assessed CBR1 protein expression and CBR1 enzymatic activity for the prototypical substrate menadione in human lymphoblastoid cell lines with distinct rs9024 genotypes. We found that hsa-miR-574-5p and hsa-miR-921 significantly decreased CBR1 protein (48% and 40%, respectively) and CBR1 menadione activity (54% and 18%, respectively) in lymphoblastoid cells homozygous for the major rs9024 G allele. In contrast, only hsa-miR-574-5p decreased CBR1 protein and CBR1 activity in cells homozygous for the minor rs9024 A allele, and did so by 49% and 56%, respectively. These results suggest that regulation of human CBR1 expression by hsa-miR-574-5p and hsa-miR-921 depends upon rs9024 genotype status.

Role of carbonyl reducing enzymes in the phase I biotransformation of the non-steroidal anti-inflammatory drug nabumetone in vitro

1. Nabumetone is a clinically used non-steroidal anti-inflammatory drug, its biotransformation includes major active metabolite 6-methoxy-2-naphtylacetic acid and another three phase I as well as corresponding phase II metabolites which are regarded as inactive. One important biotransformation pathway is carbonyl reduction, which leads to the phase I metabolite, reduced nabumetone. 2. The aim of this study is the determination of the role of a particular human liver subcellular fraction in the nabumetone reduction and the identification of participating carbonyl reducing enzymes along with their stereospecificities. 3. Both subcellular fractions take part in the carbonyl reduction of nabumetone and the reduction is at least in vitro the main biotransformation pathway. The activities of eight cytosolic carbonyl reducing enzymes--CBR1, CBR3, AKR1B1, AKR1B10, AKR1C1-4--toward nabumetone were tested. Except for CBR3, all tested reductases transform nabumetone to its reduced metabolite. AKR1C4 and AKR1C3 have the highest intrinsic clearances. 4. The stereospecificity of the majority of the tested enzymes is shifted to the production of an (+)-enantiomer of reduced nabumetone; only AKR1C1 and AKR1C4 produce predominantly an (-)-enantiomer. This project provides for the first time evidence that seven specific carbonyl reducing enzymes participate in nabumetone metabolism.

Carbonyl reductase mRNA abundance and enzymatic activity as potential biomarkers of oxidative stress in marine fish

Carbonyl reductase (CBR) is an enzyme involved in protection from oxidative stress. In rainbow trout (Oncorhynchus mykiss), the hepatic mRNA abundance of the two isoforms (A and B) is increased after exposure to treated sewage effluents, as well as after exposure with β-naphthoflavone (β-NF) and the pro-oxidant paraquat. In this study, we show that the same chemicals similarly increase the single known hepatic CBR mRNA level and CBR catalytic activity in the coastal living eelpout (Zoarces viviparus). Hepatic CBR mRNA abundance and catalytic activity were also compared between eelpout collected at contaminated and reference sites on the Swedish west coast, but no differences were observed. In conclusion, CBR is a potential biomarker candidate for monitoring the exposure and effects of AhR agonists and/or pro-oxidants in the marine environment, but more research is needed to investigate temporal regulation as well as dose dependency for different chemicals. The mRNA and enzymatic assays presented in this study provide two additional tools for researchers interested in expanding their biomarker battery.