Multiplicity of mammalian reductases for xenobiotic carbonyl compounds

Quantitative Analysis of mRNA and Protein Expression Levels of Aldo-Keto Reductase and Short-Chain Dehydrogenase/Reductase Isoforms in the Human Intestine

Enzymes catalyzing the reduction reaction of xenobiotics are mainly members of the aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase (SDR) superfamilies. The intestine, together with the liver, is responsible for first-pass effects and is an organ that determines the bioavailability of orally administered drugs. In this study, we evaluated the mRNA and protein expression levels of 12 AKR isoforms (AKR1A1, AKR1B1, AKR1B10, AKR1B15, AKR1C1, AKR1C2, AKR1C3, AKR1C4, AKR1D1, AKR1E2, AKR7A2, and AKR7A3) and 7 SDR isoforms (CBR1, CBR3, CBR4, DCXR, DHRS4, HSD11B1, and HSD17B12) in each region of the human intestine using next-generation sequencing and data-independent acquisition proteomics. At both the mRNA and protein levels, most AKR isoforms were highly expressed in the upper regions of the intestine, namely the duodenum and jejunum, and then declined toward the rectum. Among the members in the SDR superfamily, CBR1 and DHRS4 were highly expressed in the upper regions, whereas the expression levels of the other isoforms were almost uniform in all regions. Significant positive correlations between mRNA and protein levels were observed in AKR1A1, AKR1B1, AKR1B10, AKR1C3, AKR7A2, AKR7A3, CBR1, and CBR3. The mRNA level of AKR1B10 was highest, followed by AKR7A3 and CBR1, each accounting for more than 10% of the sum of all AKR and SDR levels in the small intestine. This expression profile in the human intestine was greatly different from that in the human liver, where AKR1C isoforms are predominantly expressed. SIGNIFICANCE STATEMENT: In this study comprehensively determined the mRNA and protein expression profiles of aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase isoforms involved in xenobiotic metabolism in the human intestine and found that most of them are highly expressed in the upper region, where AKR1B10, AKR7A3, and CBR1 are predominantly expressed. Since the intestine is significantly involved in the metabolism of orally administered drugs, the information provided here is valuable for pharmacokinetic studies in drug development.

In Vitro Evaluation of the Reductase Activities of Human AKR1C3 Allelic Variants

Aldo-keto reductase 1C3 (AKR1C3) plays a role in the detoxification and activation of clinical drugs by catalyzing reduction reactions. There are approximately 400 single-nucleotide polymorphisms (SNPs) in the AKR1C3 gene, but their impact on the enzyme activity is still unclear. This study aimed to clarify the effects of SNPs of AKR1C3 with more than 0.5% global minor allele frequency on the reductase activities for its typical substrates. Recombinant AKR1C3 wild-type and R66Q, E77G, C145Y, P180S, or R258C variants were constructed using insect Sf21 cells, and reductase activities for acetohexamide, doxorubicin, and loxoprofen by recombinant AKR1C3s were measured by liquid chromatography-tandem mass spectrometry. Among the variants tested, the C145Y variant showed remarkably low (6%-14% of wild type) intrinsic clearances of reductase activities for all three drugs. Reductase activities of these three drugs were measured using 34 individual Japanese liver cytosols, revealing that heterozygotes of the SNP g.55101G>A tended to show lower reductase activities for three drugs than homozygotes of the wild type. Furthermore, genotyping of the SNP g.55101G>A causing C145Y in 96 Caucasians, 166 African Americans, 192 Koreans, and 183 Japanese individuals was performed by polymerase chain reaction-restriction fragment length polymorphism. This allelic variant was specifically detected in Asians, with allele frequencies of 6.8% and 3.6% in Koreans and Japanese, respectively. To conclude, an AKR1C3 allele with the SNP g.55101G>A causing C145Y would be one of the causal factors for interindividual variabilities in the efficacy and toxicity of drugs reduced by AKR1C3. SIGNIFICANCE STATEMENT: This is the first study to clarify that the AKR1C3 allele with the SNP g.55101G>A causing C145Y results in a decrease in reductase activity. Since the allele was specifically observed in Asians, the allele would be a factor causing an interindividual variability in sensitivity of drug efficacy or toxicity of drugs reduced by AKR1C3 in Asians.

Identification of HSD17B12 as an enzyme catalyzing drug reduction reactions through investigation of nabumetone metabolism

Nabumetone, a nonsteroidal anti-inflammatory prodrug, is converted to a pharmacologically active metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA); however, it is 11-fold more efficiently converted to 4-(6-methoxy-2-naphthyl)butan-2-ol (MNBO) via a reduction reaction in human hepatocytes. The goal of this study was to identify the enzyme(s) responsible for MNBO formation from nabumetone in the human liver. MNBO formation by human liver microsomes (HLM) was 5.7-fold higher than in the liver cytosol. In a panel of 24 individual HLM samples with quantitative proteomics data, the 17β-hydroxysteroid dehydrogenase 12 (HSD17B12) protein level had the high correlation coefficient (r = 0.80, P < 0.001) among 4457 proteins quantified in microsomal fractions during MNBO formation. Recombinant HSD17B12 expressed in HEK293T cells exhibited prominent nabumetone reductase activity, and the contribution of HSD17B12 to the activity in the HLM was calculated as almost 100%. MNBO formation in HepG2 and Huh7 cells was significantly decreased by the knockdown of HSD17B12. We also examined the role of HSD17B12 in drug metabolism and found that recombinant HSD17B12 catalyzed the reduction reactions of pentoxifylline and S-warfarin, suggesting that HSD17B12 prefers compounds containing a methyl ketone group on the alkyl chain. In conclusion, our study demonstrated that HSD17B12 is responsible for the formation of MNBO from nabumetone. Together with the evidence for pentoxifylline and S-warfarin reduction, this is the first study to report that HSD17B12, which is known to metabolize endogenous compounds, such as estrone and 3-ketoacyl-CoA, plays a role as a drug-metabolizing enzyme.

Quantitative Evaluation of the Contribution of Each Aldo-Keto Reductase and Short-Chain Dehydrogenase/Reductase Isoform to Reduction Reactions of Compounds Containing a Ketone Group in the Human Liver

Enzymes of the aldo-keto reductase (AKR) and short-chain dehydrogenase/reductase superfamilies are involved in the reduction of compounds containing a ketone group. In most cases, multiple isoforms appear to be involved in the reduction of a compound, and the enzyme(s) that are responsible for the reaction in the human liver have not been elucidated. The purpose of this study was to quantitatively evaluate the contribution of each isoform to reduction reactions in the human liver. Recombinant cytosolic isoforms were constructed, i.e., AKR1C1, AKR1C2, AKR1C3, AKR1C4, and carbonyl reductase 1 (CBR1), and a microsomal isoform, 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1), and their contributions to the reduction of 10 compounds were examined by extrapolating the relative expression of each reductase protein in human liver preparations to recombinant systems quantified by liquid chromatography-mass spectrometry. The reductase activities for acetohexamide, doxorubicin, haloperidol, loxoprofen, naloxone, oxcarbazepine, and pentoxifylline were predominantly catalyzed by cytosolic isoforms, and the sum of the contributions of individual cytosolic reductases was almost 100%. Interestingly, AKR1C3 showed the highest contribution to acetohexamide and loxoprofen reduction, although previous studies have revealed that CBR1 mainly metabolizes them. The reductase activities of bupropion, ketoprofen, and tolperisone were catalyzed by microsomal isoform(s), and the contributions of HSD11B1 were calculated to be 41%, 32%, and 104%, respectively. To our knowledge, this is the first study to quantitatively evaluate the contribution of each reductase to the reduction of drugs in the human liver. SIGNIFICANCE STATEMENT: To our knowledge, this is the first study to determine the contribution of aldo-keto reductase (AKR)-1C1, AKR1C2, AKR1C3, AKR1C4, carbonyl reductase 1, and 11β-hydroxysteroid dehydrogenase type 1 to drug reductions in the human liver by utilizing the relative expression factor approach. This study found that AKR1C3 contributes to the reduction of compounds at higher-than-expected rates.

Protective Effect of Aldo-keto Reductase 1B1 Against Neuronal Cell Damage Elicited by 4'-Fluoro-α-pyrrolidinononanophenone

Chronic exposure to cathinone derivatives increases the risk of severe health hazards, whereas little is known about the detailed pathogenic mechanisms triggered by the derivatives. We have recently shown that treatment with α-pyrrolidinononanophenone (α-PNP, a highly lipophilic cathinone derivative possessing a long hydrocarbon main chain) provokes neuronal cell apoptosis and its 4'-fluorinated analog (F-α-PNP) potently augments the apoptotic effect. In this study, we found that neuronal SK-N-SH cell damage elicited by F-α-PNP treatment is augmented most potently by pre-incubation with an AKR1B1 inhibitor tolrestat, among specific inhibitors of four aldo-keto reductase (AKR) family members (1B1, 1C1, 1C2, and 1C3) expressed in the neuronal cells. In addition, forced overexpression of AKR1B1 remarkably lowered the cell sensitivity to F-α-PNP toxicity, clearly indicating that AKR1B1 protects from neurotoxicity of the derivative. Treatment of SK-N-SH cells with F-α-PNP resulted in a dose-dependent up-regulation of AKR1B1 expression and activation of its transcription factor NF-E2-related factor 2. Metabolic analyses using liquid chromatography/mass spectrometry/mass spectrometry revealed that AKR1B1 is hardly involved in the F-α-PNP metabolism. The F-α-PNP treatment resulted in production of reactive oxygen species and lipid peroxidation byproduct 4-hydroxy-2-nonenal (HNE) in the cells. The enhanced HNE level was reduced by overexpression of AKR1B1, which also lessened the cell damage elicited by HNE. These results suggest that the AKR1B1-mediated neuronal cell protection is due to detoxification of HNE formed by F-α-PNP treatment, but not to metabolism of the derivative.

Characterization of aldo-keto reductase 1C subfamily members encoded in two rat genes (akr1c19 and RGD1564865). Relationship to 9-hydroxyprostaglandin dehydrogenase

Rat genes, akr1c19 and RGD1564865, encode members (R1C19 and 20HSDL, respectively) of the aldo-keto reductase (AKR) 1C subfamily, whose functions, however, remain unknown. Here, we show that recombinant R1C19 and 20HSDL exhibit NAD⁺-dependent dehydrogenase activity for prostaglandins (PGs) with 9α-hydroxy group (PGF_2α, its 13,14-dihydro- and 15-keto derivatives, 9α,11β-PGF₂ and PGD₂). 20HSDL oxidized the PGs with much lower K_m (0.3-14 μM) and higher k_cat/K_m values (0.064-2.6 min^-1μM^-1) than those of R1C19. They also differed in other properties: R1C19, but not 20HSDL, oxidized some 17β-hydroxysteroids (5β-androstane-3α,17β-diol and 5β-androstan-17β-ol-3-one). 20HSDL was specifically inhibited by zomepirac, but not by R1C19-selective inhibitors (hexestrol, flavonoids, ibuprofen and flufenamic acid), although the two enzymes were sensitive to indomethacin and cis-unsaturated fatty acids. The mRNA for 20HSDL was expressed abundantly in rat kidney and at low levels in the liver, testis, brain, heart and colon, in contrast to ubiquitous expression of R1C19 mRNA. The comparison of enzymic features of R1C19 and 20HSDL with rat PG dehydrogenases and other AKRs suggests not only a close relationship of 20HSDL with 9-hydroxy-PG dehydrogenase in rat kidney, but also roles of R1C19 and rat AKRs (1C16 and 1C24) in the metabolism of PGF_2α, PGD₂ and 9α,11β-PGF₂ in other tissues.

Transcriptional responses in Parascaris univalens after in vitro exposure to ivermectin, pyrantel citrate and thiabendazole

Background

Parascaris univalens is a pathogenic parasite of foals and yearlings worldwide. In recent years, Parascaris spp. worms have developed resistance to several of the commonly used anthelmintics, though currently the mechanisms behind this development are unknown. The aim of this study was to investigate the transcriptional responses in adult P. univalens worms after in vitro exposure to different concentrations of three anthelmintic drugs, focusing on drug targets and drug metabolising pathways.

Methods

Adult worms were collected from the intestines of two foals at slaughter. The foals were naturally infected and had never been treated with anthelmintics. Worms were incubated in cell culture media containing different concentrations of either ivermectin (10⁻⁹ M, 10⁻¹¹ M, 10⁻¹³ M), pyrantel citrate (10⁻⁶ M, 10⁻⁸ M, 10⁻¹⁰ M), thiabendazole (10⁻⁵ M, 10⁻⁷ M, 10⁻⁹ M) or without anthelmintics (control) at 37 °C for 24 h. After incubation, the viability of the worms was assessed and RNA extracted from the anterior region of 36 worms and sequenced on an Illumina NovaSeq 6000 system.

Results

All worms were alive at the end of the incubation but showed varying degrees of viability depending on the drug and concentration used. Differential expression (Padj < 0.05 and log2 fold change ≥ 1 or ≤ − 1) analysis showed similarities and differences in the transcriptional response after exposure to the different drug classes. Candidate genes upregulated or downregulated in drug exposed worms include members of the phase I metabolic pathway short-chain dehydrogenase/reductase superfamily (SDR), flavin containing monooxygenase superfamily (FMO) and cytochrome P450-family (CYP), as well as members of the membrane transporters major facilitator superfamily (MFS) and solute carrier superfamily (SLC). Generally, different targets of the anthelmintics used were found to be upregulated and downregulated in an unspecific pattern after drug exposure, apart from the GABA receptor subunit lgc-37, which was upregulated only in worms exposed to 10⁻⁹ M of ivermectin.

Conclusions

To our knowledge, this is the first time the expression of lgc-37 and members of the FMO, SDR, MFS and SLC superfamilies have been described in P. univalens and future work should be focused on characterising these candidate genes to further explore their potential involvement in drug metabolism and anthelmintic resistance.

Dimeric dihydrodiol dehydrogenase is an efficient primate 1,5-anhydro-D-fructose reductase

1,5-Anhydro-D-fructose (AF), a metabolite of the anhydrofructose pathway of glycogen metabolism, has recently been shown to react with intracellular proteins and form advanced glycation end-products. The reactive AF is metabolized to non-reactive 1,5-anhydro-D-glucitol by AF reductase in animal tissues and human cells. Pig and mouse AF reductases were characterized, but primate AF reductase remains unknown. Here, we examined the AF-reducing activity of eleven primate NADPH-dependent reductases with broad substrate specificity for carbonyl compounds. AF was reduced by monkey dimeric dihydrodiol dehydrogenase (DHDH), human aldehyde reductase (AKR1A1) and human dicarbonyl/L-xylulose reductase (DCXR). DHDH showed the lowest K_M (21 μM) for AF, and its k_cat/K_M value (1208 s^-1mM^-1) was much higher than those of AKR1A1 (1.3 s^-1mM^-1), DCXR (1.1 s^-1mM^-1) and the pig and mouse AF reductases. AF is a novel substrate with higher affinity and catalytic efficiency than known substrates of DHDH. Docking simulation study suggested that Lys156 in the substrate-binding site of DHDH contributes to the high affinity for AF. Gene database searches identified DHDH homologues (with >95% amino acid sequence identity) in humans and apes. Thus, DHDH acts as an efficient AF reductase in primates.

The enzymology of the human prostanoid pathway

Prostanoids are short-lived autocrine and paracrine signaling molecules involved in a wide range of biological functions. They have been shown to be intimately involved in many different disease states when their regulation becomes dysfunctional. In order to fully understand the progression of any disease state or the biological functions of the well state, a complete evaluation of the genomics, proteomics, and metabolomics of the system is necessary. This review is focused on the enzymology for the enzymes involved in the synthesis of the prostanoids (prostaglandins, prostacyclins and thromboxanes). In particular, the isolation and purification of the enzymes, their enzymatic parameters and catalytic mechanisms are presented.

Pathophysiological roles of autophagy and aldo-keto reductases in development of doxorubicin resistance in gastrointestinal cancer cells

Here, we show that incubation of three human gastrointestinal cancer cell lines (HCT15, LoVo and MKN45) with doxorubicin (DOX) provokes autophagy through facilitating production of reactive oxygen species (ROS). HCT15 cell treatment with DOX resulted in up-regulation of Beclin1, down-regulation of Bcl2, activation of AMPK and JNK, and Akt inactivation, all of which were restored by pretreating with an antioxidant N-acetyl-l-cysteine. These data suggest that all the autophagy-related alterations evoked by DOX result from the ROS production. In the DOX-resistant cancer cells, degree of autophagy elicited by DOX was milder than the parental cells, and DOX treatment hardly activated the ROS-dependent apoptotic signals [formation of 4-hydroxy-2-nonenal (HNE), cytochrome-c release into cytosol, and activation of JNK and caspase-3], inferring an inverse correlation between cellular antioxidant capacity and autophagy induction by DOX. Monitoring of expression levels of aldo-keto reductases (AKRs) in the parental and DOX-resistant cells revealed an up-regulation of AKR1B10 and/or AKR1C3 with acquiring the DOX resistance. Knockdown and inhibition of AKR1B10 or AKR1C3 in these cells enhanced DOX-elicited autophagy. Measurement of DOX-reductase activity and HNE-sensitivity assay also suggested that both AKR1B10 (via high HNE-reductase activity) and AKR1C3 (via low HNE-reductase and DOX-reductase activities) are involved in the development of DOX resistance. Combination of inhibitors of autophagy and the two AKRs overcame DOX resistance and cross-resistance of gastrointestinal cancer cells with resistance development to DOX or cis-diamminedichloroplatinum. Therefore, concomitant treatment with the inhibitors may be effective as an adjuvant therapy for elevating DOX sensitivity of gastrointestinal cancer cells.

The Role of Eicosanoids in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders known. Estimates from the Alzheimer's Association suggest that there are currently 5.8 million Americans living with the disease and that this will rise to 14 million by 2050. Research over the decades has revealed that AD pathology is complex and involves a number of cellular processes. In addition to the well-studied amyloid-β and tau pathology, oxidative damage to lipids and inflammation are also intimately involved. One aspect all these processes share is eicosanoid signaling. Eicosanoids are derived from polyunsaturated fatty acids by enzymatic or non-enzymatic means and serve as short-lived autocrine or paracrine agents. Some of these eicosanoids serve to exacerbate AD pathology while others serve to remediate AD pathology. A thorough understanding of eicosanoid signaling is paramount for understanding the underlying mechanisms and developing potential treatments for AD. In this review, eicosanoid metabolism is examined in terms of in vivo production, sites of production, receptor signaling, non-AD biological functions, and known participation in AD pathology.

Metal-free defluorinative arylation of trifluoromethyl alkenes via photoredox catalysis

Literature methods to access gem-difluoroalkenes are largely limited to harsh, organometallic-based methods, and known photoredox-mediated processes are not amenable to aryl radical addition to trifluoromethyl alkenes. A metal-free, functional group-tolerant method for the preparation of benzylic gem-difluoroalkenes is described. Halogen atom abstraction from (hetero)aryl halides generates aryl radicals that undergo a defluorinative arylation of α-trifluoromethyl alkenes, tolerating electronically disparate aryl radicals and α-trifluoromethyl alkenes.

Effect of bilberry extract (Vaccinium myrtillus L.) on drug-metabolizing enzymes in rats

Vaccinium myrtillus L. (bilberry) fruit is a blue-colored berry with a high content of anthocyanins. These bioactive secondary metabolites are considered to play a major role in the health-promoting properties of bilberries. Our in vivo study was designed to assess the possible influence of bilberry extract on drug-metabolizing enzymes (DMEs). Rats were exposed to bilberry extract in drinking water at two concentrations (0.15 and 1.5 g/L). Selected DMEs were determined (mRNA expression and enzymatic activity) after 29 and 58 days in rat liver. In addition, a panel of antioxidant, physiological, biochemical and hematological parameters was studied; these parameters did not demonstrate any impact of bilberry extract on the health status of rats. A significant increase in activity was observed in cytochrome P450 (CYP) 2C11 (131% of control) and CYP2E1 (122% of control) after a 29-day administration, while the consumption of a higher concentration for a longer time led to a mild activity decrease. Slight changes were observed in some other DMEs, but they remained insignificant from a physiological perspective. According to our results, we conclude that the consumption of bilberries as a food supplement should not pose a risk of interacting with co-administered drugs based on their metabolism.

Effects of Phenelzine Administration on Mitochondrial Function, Calcium Handling, and Cytoskeletal Degradation after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) results in the production of peroxynitrite (PN), leading to oxidative damage of lipids and protein. PN-mediated lipid peroxidation (LP) results in production of reactive aldehydes 4-hydroxynonenal (4-HNE) and acrolein. The goal of these studies was to explore the hypothesis that interrupting secondary oxidative damage following a TBI via phenelzine (PZ), analdehyde scavenger, would protect against LP-mediated mitochondrial and neuronal damage. Male Sprague-Dawley rats received a severe (2.2 mm) controlled cortical impact (CCI)-TBI. PZ was administered subcutaneously (s.c.) at 15 min (10 mg/kg) and 12 h (5 mg/kg) post-injury and for the therapeutic window/delay study, PZ was administered at 1 h (10 mg/kg) and 24 h (5 mg/kg). Mitochondrial and cellular protein samples were obtained at 24 and 72 h post-injury (hpi). Administration of PZ significantly improved mitochondrial respiration at 24 and 72 h compared with vehicle-treated animals. These results demonstrate that PZ administration preserves mitochondrial bioenergetics at 24 h and that this protection is maintained out to 72 hpi. Additionally, delaying the administration still elicited significant protective effects. PZ administration also improved mitochondrial Ca2+ buffering (CB) capacity and mitochondrial membrane potential parameters compared with vehicle-treated animals at 24 h. Although PZ treatment attenuated aldehyde accumulation post-injury, the effects were insignificant. The amount of α-spectrin breakdown in cortical tissue was reduced by PZ administration at 24 h, but not at 72 hpi compared with vehicle-treated animals. In conclusion, these results indicate that acute PZ treatment successfully attenuates LP-mediated oxidative damage eliciting multiple neuroprotective effects following TBI.

The hop-derived compounds xanthohumol, isoxanthohumol and 8-prenylnaringenin are tight-binding inhibitors of human aldo-keto reductases 1B1 and 1B10

Xanthohumol (XN), a prenylated chalcone unique to hops (Humulus lupulus) and two derived prenylflavanones, isoxanthohumol (IX) and 8-prenylnaringenin (8-PN) gained increasing attention as potential anti-diabetic and cancer preventive compounds. Two enzymes of the aldo-keto reductase (AKR) superfamily are notable pharmacological targets in cancer therapy (AKR1B10) and in the treatment of diabetic complications (AKR1B1). Our results show that XN, IX and 8-PN are potent uncompetitive, tight-binding inhibitors of human aldose reductase AKR1B1 (Ki = 15.08 μM, 0.34 μM, 0.71 μM) and of human AKR1B10 (Ki = 20.11 μM, 2.25 μM, 1.95 μM). The activity of the related enzyme AKR1A1 was left unaffected by all three compounds. This is the first time these three substances have been tested on AKRs. The results of this study may provide a basis for further quantitative structure?activity relationship models and promising scaffolds for future anti-diabetic or carcinopreventive drugs.

Xylose metabolism in the pig

It is important to understand if, and to what extent, the pig can utilize xylose as an energy source if xylanase releases free xylose in the small intestine. The experimental objectives were to determine the effects of industry-relevant dietary xylose concentrations and adaptation time on xylose retention efficiency and metabolism, diet digestibility and energy value, nitrogen balance, and hindgut fermentation. Forty-eight pigs were housed in metabolism crates and randomly assigned to one of four treatments with increasing D-xylose levels (n = 12/treatment) in 2 replications of a 22-d experiment with 3 collection periods. The control diet was xylose-free (0%), to which either 2, 4, or 8% D-xylose was added. Adaptation effects were assessed during three fecal and urine collection periods: d 5-7, 12-14, and 19-21. On d 22, pigs from the 0 and 8% treatments were euthanized; cecal and colon digesta were collected. Dietary xylose did not affect the total tract digestibility of dry matter, gross energy, or crude protein (P>0.10). Digesta short chain fatty acids concentrations and molar proportions and cecal pH were not different (P>0.10). This experiment utilized a targeted metabolomics approach to characterize and quantify urine xylose and metabolite excretion. Xylose retention decreased from 60% to 47% to 41% when pigs were fed diets containing 2, 4, or 8% xylose, respectively. In the 4 and 8% treatments, xylose retention was greater in the 2nd and 3rd collection periods compared to the 1st. A comprehensive pathway for xylose metabolism was proposed and D-threitol was confirmed as the major urinary metabolite of xylose. In conclusion, pigs can metabolize xylose, but with considerably lower efficiency than glucose, and may be able to adapt with time to utilize xylose more efficiently.

Oxylipin profiling of human plasma reflects the renal dysfunction in uremic patients

INTRODUCTION

Nearly all the enzymes that mediate the metabolism of polyunsaturated fatty acids (PUFAs) are present in the kidney. However, the correlation of renal dysfunction with PUFAs metabolism in uremic patients remains unknown.

OBJECTIVES

To test whether the alterations in the metabolism of PUFAs reflect the renal dysfunction in uremic patients.

METHODS

LC-MS/MS-based oxylipin profiling was conducted for the plasma samples from the uremic patients and controls. The data were analyzed by principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA). The receiver operating characteristic (ROC) curves and the correlation of the estimated glomerular filtration rate (eGFR) with the key markers were evaluated. Furthermore, qPCR analysis of the whole blood cells was conducted to investigate the possible mechanisms. In addition, a 2nd cohort was used to validate the findings from the 1st cohort.

RESULTS

The plasma oxylipin profile distinguished the uremic patients from the controls successfully by using both PCA and OPLS-DA models. 5,6-Dihydroxyeicosatrienoic acid (5,6-DHET), 5-hydroxyeicosatetraenoic acid (5-HETE), 9(10)-epoxyoctadecamonoenoic acid [9(10)-EpOME] and 12(13)-EpOME were identified as the key markers to discriminate the patients from controls. The excellent predictive performance of these four markers was validated by ROC analysis. The eGFR significantly correlated with plasma levels of 5,6-DHET and 5-HETE positively but with plasma 9(10)-EpOME and 12(13)-EpOME negatively. The changes of these markers may account for the inactivation of cytochrome P450 2C18, 2C19, microsome epoxide hydrolase (EPHX1), and 5-lipoxygenase in the patients.

CONCLUSION

The alterations in plasma metabolic profile reflect the renal dysfunction in the uremic patients.

Detoxification Mechanism of α,β-Unsaturated Carbonyl Compounds in Cigarette Smoke Observed in Sheep Erythrocytes

Highly reactive α,β-unsaturated carbonyl compounds, such as acrolein (ACR), crotonaldehyde (CA) and methyl vinyl ketone (MVK), are environmental pollutants present in high concentrations in cigarette smoke. We have previously found that these carbonyl compounds in cigarette smoke extract (CSE) react with intracellular glutathione (GSH) to produce the corresponding GSH-ACR, GSH-CA and GSH-MVK adducts via Michael addition reaction. These adducts are then further reduced to the corresponding alcohol forms by intracellular aldo-keto reductases in highly metastatic mouse melanoma (B16-BL6) cells and then excreted into the extracellular fluid. This time, we conducted a similar study using sheep erythrocytes and found analogous changes in the sheep erythrocytes after exposure to CSE as those with B16-BL6 cells. This indicates similarity of the detoxification pathways of the α,β-unsaturated carbonyl compounds in sheep blood cells and B16-BL6 cells. Also, we found that the GSH-MVK adduct was reduced by aldose reductase in a cell-free solution to generate its alcohol form, and its reduction reaction was completely suppressed by pretreatment with epalrestat, an aldose reductase inhibitor, a member of the aldo-keto reductase family. In the presence of sheep blood cells, however, reduction of the GSH-MVK adduct was partially inhibited by epalrestat. This revealed that some member of the aldo-keto reductase superfamily other than aldose reductase is involved in reduction of the GSH-MVK adduct in sheep blood. These results suggest that blood cells, mainly erythrocytes are involved in reducing the inhalation toxicity of cigarette smoke via an aldo-keto reductase pathway other than that of aldose reductase.

Transcriptome signatures of p,p´-DDE-induced liver damage in Mus spretus mice

The use of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane) in some countries, although regulated, is contributing to an increased worldwide risk of exposure to this organochlorine pesticide or its derivative p,p'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene]. Many studies have associated p,p'-DDE exposure to type 2 diabetes, obesity and alterations of the reproductive system, but their molecular mechanisms of toxicity remain poorly understood. We have addressed this issue by using commercial microarrays based on probes for the entire Mus musculus genome to determine the hepatic transcriptional signatures of p,p'-DDE in the phylogenetically close mouse species Mus spretus. High-stringency hybridization conditions and analysis assured reliable results, which were also verified, in part, by qRT-PCR, immunoblotting and/or enzymatic activity. Our data linked 198 deregulated genes to mitochondrial dysfunction and perturbations of central signaling pathways (kinases, lipids, and retinoic acid) leading to enhanced lipogenesis and aerobic glycolysis, inflammation, cell proliferation and testosterone catabolism and excretion. Alterations of transcript levels of genes encoding enzymes involved in testosterone catabolism and excretion would explain the relationships established between p,p´-DDE exposure and reproductive disorders, obesity and diabetes. Further studies will help to fully understand the molecular basis of p,p´-DDE molecular toxicity in liver and reproductive organs, to identify effective exposure biomarkers and perhaps to design efficient p,p'-DDE exposure counteractive strategies.

Mitigating the Metabolic Liability of Carbonyl Reduction: Novel Calpain Inhibitors with P1' Extension

Dysregulation of calpains 1 and 2 has been implicated in a variety of pathological disorders including ischemia/reperfusion injuries, kidney diseases, cataract formation, and neurodegenerative diseases such as Alzheimer's disease (AD). 2-(3-Phenyl-1H)-pyrazol-1-yl)nicotinamides represent a series of novel and potent calpain inhibitors with high selectivity and in vivo efficacy. However, carbonyl reduction leading to the formation of the inactive hydroxyamide was identified as major metabolic liability in monkey and human, a pathway not reflected by routine absorption, distribution, metabolism, and excretion (ADME) assays. Using cytosolic clearance as a tailored in vitro ADME assay coupled with in vitro hepatocyte metabolism enabled the identification of analogues with enhanced stability against carbonyl reduction. These efforts led to the identification of P1' modified calpain inhibitors with significantly improved pharmacokinetic profile including P1' N-methoxyamide 23 as potential candidate compound for non-central nervous system indications.

Prediction of Drug-Drug Interactions with Bupropion and Its Metabolites as CYP2D6 Inhibitors Using a Physiologically-Based Pharmacokinetic Model

The potential of inhibitory metabolites of perpetrator drugs to contribute to drug-drug interactions (DDIs) is uncommon and underestimated. However, the occurrence of unexpected DDI suggests the potential contribution of metabolites to the observed DDI. The aim of this study was to develop a physiologically-based pharmacokinetic (PBPK) model for bupropion and its three primary metabolites—hydroxybupropion, threohydrobupropion and erythrohydrobupropion—based on a mixed “bottom-up” and “top-down” approach and to contribute to the understanding of the involvement and impact of inhibitory metabolites for DDIs observed in the clinic. PK profiles from clinical researches of different dosages were used to verify the bupropion model. Reasonable PK profiles of bupropion and its metabolites were captured in the PBPK model. Confidence in the DDI prediction involving bupropion and co-administered CYP2D6 substrates could be maximized. The predicted maximum concentration (C_max) area under the concentration-time curve (AUC) values and C_max and AUC ratios were consistent with clinically observed data. The addition of the inhibitory metabolites into the PBPK model resulted in a more accurate prediction of DDIs (AUC and C_max ratio) than that which only considered parent drug (bupropion) P450 inhibition. The simulation suggests that bupropion and its metabolites contribute to the DDI between bupropion and CYP2D6 substrates. The inhibitory potency from strong to weak is hydroxybupropion, threohydrobupropion, erythrohydrobupropion, and bupropion, respectively. The present bupropion PBPK model can be useful for predicting inhibition from bupropion in other clinical studies. This study highlights the need for caution and dosage adjustment when combining bupropion with medications metabolized by CYP2D6. It also demonstrates the feasibility of applying the PBPK approach to predict the DDI potential of drugs undergoing complex metabolism, especially in the DDI involving inhibitory metabolites.

Photoredox Generation of Carbon-Centered Radicals Enables the Construction of 1,1-Difluoroalkene Carbonyl Mimics

Described is a facile, scalable route to access functional-group-rich gem-difluoroalkenes. Using visible-light-activated catalysts in conjunction with an arsenal of carbon-radical precursors, an array of trifluoromethyl-substituted alkenes undergoes radical defluorinative alkylation. Nonstabilized primary, secondary, and tertiary radicals can be used to install functional groups in a convergent manner, which would otherwise be challenging by two-electron pathways. The process readily extends to other perfluoroalkyl-substituted alkenes. In addition, we report the development of an organotrifluoroborate reagent to expedite the synthesis of the requisite trifluoromethyl-substituted alkene starting materials.

Synthesis of Potent and Selective Inhibitors of Aldo-Keto Reductase 1B10 and Their Efficacy against Proliferation, Metastasis, and Cisplatin Resistance of Lung Cancer Cells

Aldo-keto reductase 1B10 (AKR1B10) is overexpressed in several extraintestinal cancers, particularly in non-small-cell lung cancer, where AKR1B10 is a potential diagnostic marker and therapeutic target. Selective AKR1B10 inhibitors are required because compounds should not inhibit the highly related aldose reductase that is involved in monosaccharide and prostaglandin metabolism. Currently, 7-hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-carboxylic acid benzylamide (HMPC) is known to be the most potent competitive inhibitor of AKR1B10, but it is nonselective. In this study, derivatives of HMPC were synthesized by removing the 4-methoxyphenylimino moiety and replacing the benzylamide with phenylpropylamide. Among them, 4c and 4e showed higher AKR1B10 inhibitory potency (IC₅₀ 4.2 and 3.5 nM, respectively) and selectivity than HMPC. The treatments with the two compounds significantly suppressed not only migration, proliferation, and metastasis of lung cancer A549 cells but also metastatic and invasive potentials of cisplatin-resistant A549 cells.

Impact of nonsynonymous single nucleotide polymorphisms on in-vitro metabolism of exemestane by hepatic cytosolic reductases

OBJECTIVE

Exemestane (EXE) is a potent third-generation aromatase inhibitor used as endocrine therapy in breast cancer treatment and prevention. Characterization of its metabolic pathway is incomplete, with ambiguity existing in the identity of enzymes driving the production of its key metabolite, 17β-dihydroexemestane (17β-DHE). The impact of genetic variation on EXE metabolism is also unknown. This study aims to describe cytosolic reductase involvement in hepatic EXE metabolism and to assess the impact of functional polymorphisms on metabolite production.

MATERIALS AND METHODS

Phase I metabolites were identified in incubations of EXE with pooled human liver cytosol or recombinant protein for AKR1Cs and CBR1. Kinetic parameters characterizing EXE reduction were measured for purified wild-type enzymes, and nonsynonymous variants occurring at greater than 1% minor allele frequency using UPLC/MS/MS.

RESULTS

Human liver cytosol, CBR1, AKR1C1, AKR1C2, AKR1C3, and AKR1C4 reduce EXE to active primary metabolite 17β-DHE. The formation of a novel metabolite, 17α-DHE, was catalyzed by recombinant AKR1C4 and CBR1 in addition to hepatic cytosol. Variants AKR1C3 Arg258Cys and AKR1C4 Gly135Glu had significantly decreased affinity for EXE relative to their respective wild types. Five common AKR1C3 polymorphisms were associated with decreased rates of catalysis, whereas AKR1C4 Gly135Glu increased the velocity of EXE reduction.

CONCLUSION

AKR1Cs and CBR1 catalyze EXE reduction in vitro. These results imply that cytosolic ketosteroid reductases may participate in the EXE metabolic pathway in vivo. In addition, several common variants were associated with altered enzymatic activity, suggesting that functional polymorphisms could play an important role in overall EXE metabolism and activity by altering the extent and duration of 17β-DHE exposure.

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.

Metabolism of bupropion by carbonyl reductases in liver and intestine

Bupropion's metabolism and the formation of hydroxybupropion in the liver by cytochrome P450 2B6 (CYP2B6) has been extensively studied; however, the metabolism and formation of erythro/threohydrobupropion in the liver and intestine by carbonyl reductases (CR) has not been well characterized. The purpose of this investigation was to compare the relative contribution of the two metabolism pathways of bupropion (by CYP2B6 and CR) in the subcellular fractions of liver and intestine and to identify the CRs responsible for erythro/threohydrobupropion formation in the liver and the intestine. The results showed that the liver microsome generated the highest amount of hydroxybupropion (Vmax = 131 pmol/min per milligram, Km = 87 μM). In addition, liver microsome and S9 fractions formed similar levels of threohydrobupropion by CR (Vmax = 98-99 pmol/min per milligram and Km = 186-265 μM). Interestingly, the liver has similar capability to form hydroxybupropion (by CYP2B6) and threohydrobupropion (by CR). In contrast, none of the intestinal fractions generate hydroxybupropion, suggesting that the intestine does not have CYP2B6 available for metabolism of bupropion. However, intestinal S9 fraction formed threohydrobupropion to the extent of 25% of the amount of threohydrobupropion formed by liver S9 fraction. Enzyme inhibition and Western blots identified that 11β-dehydrogenase isozyme 1 in the liver microsome fraction is mainly responsible for the formation of threohydrobupropion, and in the intestine AKR7 may be responsible for the same metabolite formation. These quantitative comparisons of bupropion metabolism by CR in the liver and intestine may provide new insight into its efficacy and side effects with respect to these metabolites.

Bioactivation of loxoprofen to a pharmacologically active metabolite and its disposition kinetics in human skin

Loxoprofen (LX) is a prodrug-type non-steroidal anti-inflammatory drug which is used not only as an oral drug but also as a transdermal formulation. As a pharmacologically active metabolite, the trans-alcohol form of LX (trans-OH form) is generated after oral administration to humans. The objectives of this study were to evaluate the generation of the trans-OH form in human in vitro skin and to identify the predominant enzyme for its generation. In the permeation and metabolism study using human in vitro skin, both the permeation of LX and the formation of the trans-OH form increased in a time- and dose-dependent manner after the application of LX gel to the skin. In addition, the characteristics of permeation and metabolism of both LX and the trans-OH form were examined by a mathematical pharmacokinetic model. The K_m value was calculated to be 10.3 mm in the human in vitro skin. The predominant enzyme which generates the trans-OH form in human whole skin was identified to be carbonyl reductase 1 (CBR1) by immunodepletion using the anti-human CBR1 antibody. The results of the enzyme kinetic study using the recombinant human CBR1 protein demonstrated that the K_m and V_max values were 7.30 mm and 402 nmol/min/mg protein, respectively. In addition, it was found that no unknown metabolites were generated in the human in vitro skin. This is the first report in which LX is bioactivated to the trans-OH form in human skin by CBR1. Copyright © 2015 John Wiley & Sons, Ltd.

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 functional antioxidant responsive element in the promoter of the Chinese hamster carbonyl reductase 3 (Chcr3) gene

CHCR3, a member of the short-chain dehydrogenase/reductase superfamily, is a carbonyl reductase 3 enzyme in Chinese hamsters. Carbonyl reductase 3 in humans has been believed to involve the metabolism and/or pharmacokinetics of anthracycline drugs, and the mechanism underlying the gene regulation has been investigated. In this study, the nucleotide sequence of the Chcr3 promoter was originally determined, and its promoter activity was characterised. The proximal promoter region is TATA-less and GC-rich, similar to the promoter region of human carbonyl reductase 3. Cobalt stimulated the transcriptional activity of the Chcr3 gene. The results of a luciferase gene reporter assay demonstrated that cobalt-induced stimulation required an antioxidant responsive element. Forced expression of Nrf2, the transcription factor that binds to antioxidant responsive elements, enhanced the transcriptional activity of the Chcr3 gene. These results suggest that cobalt induces the expression of the Chcr3 gene via the Nrf2-antioxidant responsive element pathway.

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.

Effect of experimental kidney disease on the functional expression of hepatic reductases

Chronic kidney disease (CKD) affects the nonrenal clearance of drugs by modulating the functional expression of hepatic drug-metabolizing enzymes and transporters. The impact of CKD on oxidative and conjugative metabolism has been extensively studied. However, its effect on hepatic drug reduction, an important phase I drug-metabolism pathway, has not been investigated. We aimed to assess the effect of experimental CKD on hepatic reduction using warfarin as a pharmacological probe substrate. Cytosolic and microsomal cellular fractions were isolated from liver tissue harvested from five-sixths-nephrectomized and control rats (n = 10 per group). The enzyme kinetics for warfarin reduction were evaluated in both fractions, and formation of warfarin alcohols was used as an indicator of hepatic reductase activity. Selective inhibitors were employed to identify reductases involved in warfarin reduction. Gene and protein expression of reductases were determined using quantitative real-time polymerase chain reaction and Western blotting, respectively. Formation of RS/SR-warfarin alcohol was decreased by 39% (P < 0.001) and 43% (P < 0.01) in cytosol and microsomes, respectively, in CKD rats versus controls. However, RR/SS-warfarin alcohol formation was unchanged in the cytosol, and a trend toward its decreased production was observed in microsomes. Gene and protein expression of cytosolic carbonyl reductase 1 and aldo-keto reductase 1C3/18, and microsomal 11β-hydroxysteroid dehydrogenase type 1 were significantly reduced by >30% (P < 0.05) in CKD rats compared with controls. Collectively, these results suggest that the functional expression of hepatic reductases is selectively decreased in kidney disease. Our findings may explain one mechanism for altered nonrenal clearance, exposure, and response of drugs in CKD patients.

Effects of Sublethal Exposure to a Glyphosate-Based Herbicide Formulation on Metabolic Activities of Different Xenobiotic-Metabolizing Enzymes in Rats

The activities of different xenobiotic-metabolizing enzymes in liver subcellular fractions from Wistar rats exposed to a glyphosate (GLP)-based herbicide (Roundup full II) were evaluated in this work. Exposure to the herbicide triggered protective mechanisms against oxidative stress (increased glutathione peroxidase activity and total glutathione levels). Liver microsomes from both male and female rats exposed to the herbicide had lower (45%-54%, P < 0.01) hepatic cytochrome P450 (CYP) levels compared to their respective control animals. In female rats, the hepatic 7-ethoxycoumarin O-deethylase (a general CYP-dependent enzyme activity) was 57% higher (P < 0.05) in herbicide-exposed compared to control animals. Conversely, this enzyme activity was 58% lower (P < 0.05) in male rats receiving the herbicide. Lower (P < 0.05) 7-ethoxyresorufin O-deethlyase (EROD, CYP1A1/2 dependent) and oleandomycin triacetate (TAO) N-demethylase (CYP3A dependent) enzyme activities were observed in liver microsomes from exposed male rats. Conversely, in females receiving the herbicide, EROD increased (123%-168%, P < 0.05), whereas TAO N-demethylase did not change. A higher (158%-179%, P < 0.01) benzyloxyresorufin O-debenzylase (a CYP2B-dependent enzyme activity) activity was only observed in herbicide-exposed female rats. In herbicide-exposed rats, the hepatic S-oxidation of methimazole (flavin monooxygenase dependent) was 49% to 62% lower (P < 0.001), whereas the carbonyl reduction of menadione (a cytosolic carbonyl reductase-dependent activity) was higher (P < 0.05). Exposure to the herbicide had no effects on enzymatic activities dependent on carboxylesterases, glutathione transferases, and uridinediphospho-glucuronosyltransferases. This research demonstrated certain biochemical modifications after exposure to a GLP-based herbicide. Such modifications may affect the metabolic fate of different endobiotic and xenobiotic substances. The pharmacotoxicological significance of these findings remains to be clarified.

Exposure to 9,10-phenanthrenequinone accelerates malignant progression of lung cancer cells through up-regulation of aldo-keto reductase 1B10

Inhalation of 9,10-phenanthrenequinone (9,10-PQ), a major quinone in diesel exhaust, exerts fatal damage against a variety of cells involved in respiratory function. Here, we show that treatment with high concentrations of 9,10-PQ evokes apoptosis of lung cancer A549 cells through production of reactive oxygen species (ROS). In contrast, 9,10-PQ at its concentrations of 2 and 5 μM elevated the potentials for proliferation, invasion, metastasis and tumorigenesis, all of which were almost completely inhibited by addition of an antioxidant N-acetyl-l-cysteine, inferring a crucial role of ROS in the overgrowth and malignant progression of lung cancer cells. Comparison of mRNA expression levels of six aldo-keto reductases (AKRs) in the 9,10-PQ-treated cells advocated up-regulation of AKR1B10 as a major cause contributing to the lung cancer malignancy. In support of this, the elevation of invasive, metastatic and tumorigenic activities in the 9,10-PQ-treated cells was significantly abolished by the addition of a selective AKR1B10 inhibitor oleanolic acid. Intriguingly, zymographic and real-time PCR analyses revealed remarkable increases in secretion and expression, respectively, of matrix metalloproteinase 2 during the 9,10-PQ treatment, and suggested that the AKR1B10 up-regulation and resultant activation of mitogen-activated protein kinase cascade are predominant mechanisms underlying the metalloproteinase induction. In addition, HPLC analysis and cytochrome c reduction assay in in vitro 9,10-PQ reduction by AKR1B10 demonstrated that the enzyme catalyzes redox-cycling of this quinone, by which ROS are produced. Collectively, these results suggest that AKR1B10 is a key regulator involved in overgrowth and malignant progression of the lung cancer cells through ROS production due to 9,10-PQ redox-cycling.