Epoxide hydrolases: their roles and interactions with lipid metabolism

Dendrogenin A arises from cholesterol and histamine metabolism and shows cell differentiation and anti-tumour properties

We previously synthesized dendrogenin A and hypothesized that it could be a natural metabolite occurring in mammals. Here we explore this hypothesis and report the discovery of dendrogenin A in mammalian tissues and normal cells as an enzymatic product of the conjugation of 5,6α-epoxy-cholesterol and histamine. Dendrogenin A was not detected in cancer cell lines and was fivefold lower in human breast tumours compared with normal tissues, suggesting a deregulation of dendrogenin A metabolism during carcinogenesis. We established that dendrogenin A is a selective inhibitor of cholesterol epoxide hydrolase and it triggered tumour re-differentiation and growth control in mice and improved animal survival. The properties of dendrogenin A and its decreased level in tumours suggest a physiological function in maintaining cell integrity and differentiation. The discovery of dendrogenin A reveals a new metabolic pathway at the crossroads of cholesterol and histamine metabolism and the existence of steroidal alkaloids in mammals.

It has been hypothesized that the steroidal alkaloid dendrogenin A (DDA) is a natural metabolite. de Medina et al. show that DDA is produced in mammalian tissues from 5,6α-epoxy-cholesterol and histamine metabolism, and that the compound displays cell differentiation and anti-tumour activities.

Stabilized epoxygenated fatty acids regulate inflammation, pain, angiogenesis and cancer

Epoxygenated fatty acids (EpFAs), which are lipid mediators produced by cytochrome P450 epoxygenases from polyunsaturated fatty acids, are important signaling molecules known to regulate various biological processes including inflammation, pain and angiogenesis. The EpFAs are further metabolized by soluble epoxide hydrolase (sEH) to form fatty acid diols which are usually less-active. Pharmacological inhibitors of sEH that stabilize endogenous EpFAs are being considered for human clinical uses. Here we review the biology of ω-3 and ω-6 EpFAs on inflammation, pain, angiogenesis and tumorigenesis.

Eicosapentaenoic acid is converted via ω-3 epoxygenation to the anti-inflammatory metabolite 12-hydroxy-17,18-epoxyeicosatetraenoic acid

Eicosapentaenoic acid (EPA) has beneficial effects in many inflammatory disorders. In this study, dietary EPA was converted to 17,18-epoxyeicosatetraenoic acid (17,18-EpETE) by ω-3 epoxygenation in the mouse peritoneal cavity. Mediator lipidomics revealed a series of novel oxygenated metabolites of 17,18-EpETE, and one of the major metabolites, 12-hydroxy-17,18-epoxyeicosatetraenoic acid (12-OH-17,18-EpETE), displayed a potent anti-inflammatory action by limiting neutrophil infiltration in murine zymosan-induced peritonitis. 12-OH-17,18-EpETE inhibited leukotriene B4-induced neutrophil chemotaxis and polarization in vitro in a low nanomolar range (EC50 0.6 nM). The complete structures of two natural isomers were assigned as 12S-OH-17R,18S-EpETE and 12S-OH-17S,18R-EpETE, using chemically synthesized stereoisomers. These natural isomers displayed potent anti-inflammatory action, whereas the unnatural stereoisomers were essentially devoid of activity. These results demonstrate that 17,18-EpETE derived from dietary EPA is converted to a potent bioactive metabolite 12-OH-17,18-EpETE, which may generate an endogenous anti-inflammatory metabolic pathway.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

mEH Tyr113His polymorphism and the risk of ovarian cancer development

Background

The causes of ovarian cancer are complex and may be influenced by many factors, including polymorphism in the microsomal epoxide hydrolase (mEH) gene. Previous work suggests an association between the Tyr113His mEH polymorphism rs1051740 and susceptibility to ovarian cancer, but the results have been inconsistent.

Methods

PubMed, EMBASE, Google Scholar, and Chinese National Knowledge Infrastructure databases were systematically searched to identify relevant studies. A meta-analysis was performed to examine the association between Tyr113His mEH polymorphism and susceptibility to ovarian cancer. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated.

Results

Five studies involving 2,566 cases and 2,839 controls were included. Although the polymorphism did not affect ovarian cancer risk in the allelic contrast model (OR = 0.99, 95% CI = 0.83-1.17, P = 0.86), the mutant CC genotype was significantly associated with increased risk in the homozygote comparison (OR = 1.20, 95% CI = 1.01-1.43, P = 0.04) and recessive genetic models (OR = 1.20, 95% CI = 1.01-1.41, P = 0.03). The wild-type TT genotype was not associated with higher or lower ovarian cancer risk in the dominant genetic model (OR = 1.04, 95% CI = 0.83-1.29, P = 0.74). These results were robust to sensitivity analysis.

Conclusions

The CC genotype of Tyr113His mEH may confer increased risk of ovarian cancer. These conclusions should be verified in large and well-designed studies.

Identification of host proteins modulated by the virulence factor AC2 of Tomato chlorotic mottle virus in Nicotiana benthamiana

Tomato, one of the most important crops cultivated worldwide, has been severely affected by begomoviruses such as the Tomato chlorotic mottle virus (ToCMoV). Virulence factor AC2 is considered crucial for a successful virus-plant interaction and is known to act as a transcriptional activator and in some begomoviruses to function as an RNA silencing suppressor factor. However, the exact functions of the AC2 protein of the begomovirus ToCMoV are not yet established. The aim of the present study was to identify differentially expressed proteins of the model plant Nicotiana benthamiana in response to the expression of the AC2 gene, isolated from ToCMoV. N. benthamiana plants were inoculated with Agrobacterium tumefaciens containing the viral vector Potato virus X (PVX) and with the PVX-AC2 construction. 2DE was performed and proteins were identified by MS. The results showed that the expression of ToCMoV AC2 alters the levels of several host proteins, which are important for normal plant development, causing an imbalance in cellular homeostasis. This study highlights the effect of AC2 in the modulation of plant defense processes by increasing the expression of several oxidative stress-related and pathogenesis-related proteins, as well as its role in modulating the proteome of the photosynthesis and energy production systems.

Molecular characterization of NbEH1 and NbEH2, two epoxide hydrolases from Nicotiana benthamiana

Plant epoxide hydrolases (EH) form two major clades, named EH1 and EH2. To gain a better understanding of the biochemical roles of the two classes, NbEH1.1 and NbEH2.1 were isolated from Nicotiana benthamiana and StEH from potato and heterologously expressed in Escherichia coli. The purified recombinant proteins were assayed with a variety of substrates. NbEH1.1 only accepted some aromatic epoxides, and displayed the highest enzyme activity towards phenyl glycidyl ether. In contrast, NbEH2.1 displayed a broad substrate range and similar substrate specificity as StEH. The latter enzymes showed activity towards all fatty acid epoxides examined. The activity (Vmax) of NbEH1.1 towards phenyl glycidyl ether was 10 times higher than that of NbEH2.1. On the contrary, NbEH2.1 converted cis-9,10-epoxystearic acid with Vmax of 3.83μmolminmg(-1) but NbEH1.1 could not hydrolyze cis-9,10-epoxystearic acid. Expression analysis revealed that NbEH1.1 is induced by infection with tobacco mosaic virus (TMV) and wounding, whereas NbEH2.1 is present at a relatively constant level, not influenced by treatment with TMV and wounding. NbEH1.1 transcripts were present predominantly in roots, whereas NbEH2.1 mRNAs were detected primarily in leaves and stems. Overall, these two types of tobacco EH enzymes are distinguished not only by their gene expression, but also by different substrate specificities. EH1 seems not to participate in cutin biosynthesis and it may play a role in generating signals for activation of certain defence and stress responses in tobacco. However, members of the EH2 group hydrate fatty acid epoxides and may be involved in cutin monomer production in plants.

Expression of a novel mRNA transcript for human microsomal epoxide hydrolase (EPHX1) is regulated by short open reading frames within its 5'-untranslated region

Microsomal epoxide hydrolase (mEH, EPHX1) is a critical xenobiotic-metabolizing enzyme, catalyzing both detoxification and bioactivation reactions that direct the disposition of chemical epoxides, including the carcinogenic metabolites of several polycyclic aromatic hydrocarbons. Recently, we discovered that a previously unrecognized and primate-specific EPHX1 transcript, termed E1-b, was actually the predominant driver of EPHX1 expression in all human tissues. In this study, we identify another human EPHX1 transcript, designated as E1-b'. Unusually, both the E1-b and E1-b' mRNA transcripts are generated from the use of a far upstream gene promoter, localized ∼18.5 kb 5'-upstream of the EPHX1 protein-coding region. Although expressed at comparatively lower levels than E1-b, the novel E1-b' transcript is readily detected in all tissues examined, with highest levels maintained in human ovary. The E1-b' mRNA possesses unusual functional features in its 5'-untranslated region, including a GC-rich leader sequence and two upstream AUGs that encode for short peptides of 26 and 17 amino acids in length, respectively. Results from in vitro transcription/translation assays and direct transfection in mammalian cells of either the E1-b' transcript or the encoded peptides demonstrated that the E1-b' upstream open reading frames (uORFs) are functional, with their presence markedly inhibiting the translation of EPHX1 protein, both in cis and in trans configurations. These unique uORF peptides exhibit no homology to any other known uORF sequences but likely function to mediate post-transcription regulation of EPHX1 and perhaps more broadly as translational regulators in human cells.

Soluble epoxide hydrolase: gene structure, expression and deletion

Mammalian soluble epoxide hydrolase (sEH) converts epoxides to their corresponding diols through the addition of a water molecule. sEH readily hydrolyzes lipid signaling molecules, including the epoxyeicosatrienoic acids (EETs), epoxidized lipids produced from arachidonic acid by the action of cytochrome p450s. Through its metabolism of the EETs and other lipid mediators, sEH contributes to the regulation of vascular tone, nociception, angiogenesis and the inflammatory response. Because of its central physiological role in disease states such as cardiac hypertrophy, diabetes, hypertension, and pain sEH is being investigated as a therapeutic target. This review begins with a brief introduction to sEH protein structure and function. sEH evolution and gene structure are then discussed before human small nucleotide polymorphisms and mammalian gene expression are described in the context of several disease models. The review ends with an overview of studies that have employed the sEH knockout mouse model.

Soluble epoxide hydrolase deficiency or inhibition attenuates diet-induced endoplasmic reticulum stress in liver and adipose tissue

Soluble epoxide hydrolase (sEH) is a cytosolic enzyme whose inhibition has beneficial effects in cardiovascular, inflammatory, and metabolic diseases in murine models. Mice with targeted deletion or pharmacological inhibition of sEH exhibit improved insulin signaling in liver and adipose tissue. Herein, we assessed the role of sEH in regulating endoplasmic reticulum (ER) stress in liver and adipose tissue. We report that sEH expression was increased in the livers and adipose tissue of mice fed a high fat diet, the adipose tissue of overweight humans, and palmitate-treated cells. Importantly, sEH deficiency or inhibition in mice attenuated chronic high fat diet-induced ER stress in liver and adipose tissue. Similarly, pharmacological inhibition of sEH in HepG2 cells and 3T3-L1 adipocytes mitigated chemical-induced ER stress and activation of JNK, p38, and cell death. In addition, insulin signaling was enhanced in HepG2 cells treated with sEH substrates and attenuated in cells treated with sEH products. In summary, these findings demonstrate that sEH is a physiological modulator of ER stress and a potential target for mitigating complications associated with obesity.

Epoxy metabolites of docosahexaenoic acid (DHA) inhibit angiogenesis, tumor growth, and metastasis

Epidemiological and preclinical evidence supports that omega-3 dietary fatty acids (fish oil) reduce the risks of macular degeneration and cancers, but the mechanisms by which these omega-3 lipids inhibit angiogenesis and tumorigenesis are poorly understood. Here we show that epoxydocosapentaenoic acids (EDPs), which are lipid mediators produced by cytochrome P450 epoxygenases from omega-3 fatty acid docosahexaenoic acid, inhibit VEGF- and fibroblast growth factor 2-induced angiogenesis in vivo, and suppress endothelial cell migration and protease production in vitro via a VEGF receptor 2-dependent mechanism. When EDPs (0.05 mg · kg(-1) · d(-1)) are coadministered with a low-dose soluble epoxide hydrolase inhibitor, EDPs are stabilized in circulation, causing ~70% inhibition of primary tumor growth and metastasis. Contrary to the effects of EDPs, the corresponding metabolites derived from omega-6 arachidonic acid, epoxyeicosatrienoic acids, increase angiogenesis and tumor progression. These results designate epoxyeicosatrienoic acids and EDPs as unique endogenous mediators of an angiogenic switch to regulate tumorigenesis and implicate a unique mechanistic linkage between omega-3 and omega-6 fatty acids and cancers.

Substituted phenyl groups improve the pharmacokinetic profile and anti-inflammatory effect of urea-based soluble epoxide hydrolase inhibitors in murine models

Soluble epoxide hydrolase inhibitors (sEHIs) are anti-inflammatory, analgesic, anti-hypertensive, cardio- and renal-protective in multiple animal models. However, the earlier adamantyl-containing urea-based inhibitors are rapidly metabolized. Therefore, new potent inhibitors with the adamantyl group replaced by a substituted phenyl group were synthesized to presumptively offer better pharmacokinetic (PK) properties. Here we describe the improved PK profile of these inhibitors and the anti-inflammatory effect of the most promising one in a murine model. The PK profiles of inhibitors were determined following p.o. administration and serial bleeding in mice. The anti-inflammatory effect of 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea (TPPU), the most promising inhibitor among the five sEHIs tested, was investigated in a lipopolysaccharide (LPS)-challenged murine model. The earlier broadly-used adamantyl-containing sEHI, trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), was used for comparison. Compared with the earlier adamantyl-containing urea-based inhibitors, substituted phenyl-containing urea-based inhibitors afford more favorable PK properties, such as higher Cmaxs, larger AUCs and longer t1/2s, which, as expected, show more stable metabolic stability. Moreover, oral administration of TPPU dramatically reversed the shifts caused by LPS-challenge in plasma levels of inflammatory cytokines, epoxides and corresponding diols, which is more potent than t-AUCB. The substituted phenyl-containing sEHIs are more metabolically stable than those with adamantyl group, resulting in more potent efficacy in vivo. This indicates a new strategy for development of sEHIs for further study toward clinical trials.

Measurement of soluble epoxide hydrolase (sEH) activity

The human soluble epoxide hydrolase (sEH; EC 3.3.3.2) is the product of the EXPH2 gene. The sEH catalyzes the addition of a water molecule to an epoxide, resulting in the corresponding diol. Early work suggested a role of sEH in detoxifying a wide array of xenobiotic epoxides; however, recent findings clearly implicate the sEH in the regulation of blood pressure, pain, and inflammation through the hydrolysis of endogenous epoxy fatty acids such as epoxyeicosatrienoic acids (EETs). Both expression and activity of sEH are influenced by a wide array of xenobiotics, underlying how environmental contaminants could influence human health through sEH. This unit describes radiometric, fluorimetric, and mass spectrometric assays for measuring the activity of sEH and its inhibition.

Meta-analysis of microsomal epoxide hydrolase gene polymorphism and risk of hepatocellular carcinoma

Background

Hepatocarcinogenesis is a complex process that may be influenced by many factors, including polymorphism in microsomal epoxide hydrolase (mEH). Previous work suggests an association between the Tyr113His and His139Arg mEH polymorphisms and susceptibility to hepatocellular carcinoma (HCC), but the results have been inconsistent.

Methods

PubMed, EMBASE, Google Scholar and the Chinese National Knowledge Infrastructure databases were systematically searched to identify relevant studies. A meta-analysis was performed to examine the association between Tyr113His and His139Arg mEH polymorphism and susceptibility to HCC. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

Results

Eleven studies were included in the meta-analysis, involving 1,696 HCC cases and 3,600 controls. The 113His- mEH allele was significantly associated with increased risk of HCC based on allelic contrast (OR = 1.35, 95% CI = 1.04–1.75, p = 0.02), homozygote comparison (OR = 1.65, 95% CI = 1.07–2.54, p = 0.02) and a recessive genetic model (OR = 1.54, 95% CI = 1.21–1.96, p<0.001), while individuals carrying the Arg139Arg mEH genotype had no association with increased or decreased risk of HCC.

Conclusion

The 113His- allele polymorphism in mEH may be a risk factor for hepatocarcinogenesis, while the mEH 139Arg- allele may not be a risk or protective factor. There is substantial evidence that mEH polymorphisms interact synergistically with other genes and the environment to modulate risk of HCC. Further large and well-designed studies are needed to confirm these conclusions.

Development of On-line Liquid Chromatography-Biochemical Detection for Soluble Epoxide Hydrolase Inhibitors in Mixtures

In this study, an end-point-based fluorescence assay for soluble epoxide hydrolase (sEH) was transformed into an on-line continuous-flow format. The on-line biochemical detection system (BCD) was coupled on-line to liquid chromatography (LC) to allow mixture analysis. The on-line BCD was based on a flow system wherein sEH activity was detected by competition of analytes with the substrate hydrolysis. The reaction product was measured by fluorescence detection. In parallel to the BCD data, UV and MS data were obtained through post-column splitting of the LC effluent. The buffer system and reagent concentrations were optimized resulting in a stable on-line BCD with a good assay window and good sensitivity (S/N > 60). The potency of known sEH inhibitors (sEHis) obtained by LC-BCD correlates well with published values. The LC-BCD system was applied to test how oxidative microsomal metabolism affects the potency of three sEHis. After incubation with pig liver microsomes, several metabolites of sEHis were characterized by MS, while their individual potencies were measured by BCD. For all compounds tested, active metabolites were observed. The developed method allows for the first time the detection of sEHis in mixtures providing new opportunities in the development of drug candidates.

Genome-wide association study dissects the genetic architecture of oil biosynthesis in maize kernels

Maize kernel oil is a valuable source of nutrition. Here we extensively examine the genetic architecture of maize oil biosynthesis in a genome-wide association study using 1.03 million SNPs characterized in 368 maize inbred lines, including 'high-oil' lines. We identified 74 loci significantly associated with kernel oil concentration and fatty acid composition (P < 1.8 × 10(-6)), which we subsequently examined using expression quantitative trait loci (QTL) mapping, linkage mapping and coexpression analysis. More than half of the identified loci localized in mapped QTL intervals, and one-third of the candidate genes were annotated as enzymes in the oil metabolic pathway. The 26 loci associated with oil concentration could explain up to 83% of the phenotypic variation using a simple additive model. Our results provide insights into the genetic basis of oil biosynthesis in maize kernels and may facilitate marker-based breeding for oil quantity and quality.

Förster resonance energy transfer competitive displacement assay for human soluble epoxide hydrolase

The soluble epoxide hydrolase (sEH), responsible for the hydrolysis of various fatty acid epoxides to their corresponding 1,2-diols, is becoming an attractive pharmaceutical target. These fatty acid epoxides, particularly epoxyeicosatrienoic acids (EETs), play an important role in human homeostatic and inflammation processes. Therefore, inhibition of human sEH, which stabilizes EETs in vivo, brings several beneficial effects to human health. Although there are several catalytic assays available to determine the potency of sEH inhibitors, measuring the in vitro inhibition constant (K(i)) for these inhibitors using catalytic assay is laborious. In addition, k(off), which has been recently suggested to correlate better with the in vivo potency of inhibitors, has never been measured for sEH inhibitors. To better measure the potency of sEH inhibitors, a reporting ligand, 1-(adamantan-1-yl)-3-(1-(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)acetyl) piperidin-4-yl)urea (ACPU), was designed and synthesized. With ACPU, we have developed a Förster resonance energy transfer (FRET)-based competitive displacement assay using intrinsic tryptophan fluorescence from sEH. In addition, the resulting assay allows us to measure the K(i) values of very potent compounds to the picomolar level and to obtain relative k(off) values of the inhibitors. This assay provides additional data to evaluate the potency of sEH inhibitors.

Development of an HTS assay for EPHX2 phosphatase activity and screening of nontargeted libraries

The EPXH2 gene encodes soluble epoxide hydrolase (sEH), which has two distinct enzyme activities: epoxide hydrolase (Cterm-EH) and phosphatase (Nterm-phos). The Cterm-EH is involved in the metabolism of arachidonic acid epoxides that play important roles in blood pressure, cell growth, inflammation, and pain. While recent findings suggested complementary biological roles for Nterm-phos, research is limited by the lack of potent bioavailable inhibitors of this phosphatase activity. Also, a potent bioavailable inhibitor of this activity could be important in the development of therapy for cardiovascular diseases. We report herein the development of an HTS enzyme-based assay for Nterm-phos (Z'>0.9) using AttoPhos as the substrate. This assay was used to screen a wide variety of chemical entities, including a library of known drugs that have reached through clinical evaluation (Pharmakon 1600), as well as a library of pesticides and environmental toxins. We discovered that ebselen inhibits sEH phosphatase activity. Ebselen binds to the N-terminal domain of sEH (K(I)=550 nM) and chemically reacts with the enzyme to quickly and irreversibly inhibit Nterm-phos, and subsequently Cterm-EH, and thus represents a new class of sEH inhibitor.

Synthesis and structure-activity relationship of piperidine-derived non-urea soluble epoxide hydrolase inhibitors

A series of potent amide non-urea inhibitors of soluble epoxide hydrolase (sEH) is disclosed. The inhibition of soluble epoxide hydrolase leads to elevated levels of epoxyeicosatrienoic acids (EETs), and thus inhibitors of sEH represent one of a novel approach to the development of vasodilatory and anti-inflammatory drugs. Structure-activities studies guided optimization of a lead compound, identified through high-throughput screening, gave rise to sub-nanomolar inhibitors of human sEH with stability in human liver microsomal assay suitable for preclinical development.

Adenosine A2A receptor modulates vascular response in soluble epoxide hydrolase-null mice through CYP-epoxygenases and PPARγ

The interaction between adenosine and soluble epoxide hydrolase (sEH) in vascular response is not known. Therefore, we hypothesized that lack of sEH in mice enhances adenosine-induced relaxation through A(2A) adenosine receptors (AR) via CYP-epoxygenases and peroxisome proliferator-activated receptor γ (PPARγ). sEH(-/-) showed an increase in A(2A) AR, CYP2J, and PPARγ by 31%, 65%, and 36%, respectively, and a decrease in A(1)AR and PPARα (30% and 27%, respectively) vs. sEH(+/+). 5'-N-ethylcarboxamidoadenosine (NECA, an adenosine receptor agonist), CGS 21680 (A(2A) AR-agonist), and GW 7647 (PPARα-agonist)-induced responses were tested with nitro-l-arginine methyl ester (l-NAME) (NO-inhibitor; 10(-4) M), ZM-241385, SCH-58261 (A(2A) AR-antagonists; 10(-6) M), 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, an epoxyeicosatrienoic acid-antagonist; 10(-5) M), 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA; 10 μM) or trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB, sEH-inhibitors; 10(-5) M), and T0070907 (PPARγ-antagonist; 10(-7) M). In sEH(-/-) mice, ACh response was not different from sEH(+/+) (P > 0.05), and l-NAME blocked ACh-responses in both sEH(-/-) and sEH(+/+) mice (P < 0.05). NECA (10(-6) M)-induced relaxation was higher in sEH(-/-) (+12.94 ± 3.2%) vs. sEH(+/+) mice (-5.35 ± 5.2%); however, it was blocked by ZM-241385 (-22.42 ± 1.9%) and SCH-58261(-30.04 ± 4.2%). CGS-21680 (10(-6) M)-induced relaxation was higher in sEH(-/-) (+37.4 ± 5.4%) vs. sEH(+/+) (+2.14 ± 2.8%). l-NAME (sEH(-/-), +30.28 ± 4.8%, P > 0.05) did not block CGS-21680-induced response, whereas 14,15-EEZE (-7.1 ± 3.7%, P < 0.05) did. Also, AUDA and t-AUCB did not change CGS-21680-induced response in sEH(-/-) (P > 0.05), but reversed in sEH(+/+) (from +2.14 ± 2.8% to +45.33 ± 4.1%, and +63.37 ± 7.2, respectively). PPARα-agonist did not relax as CGS 21680 (-2.48 ± 1.1 vs. +37.4 ± 5.4%) in sEH(-/-), and PPARγ-antagonist blocked (from +37.4 ± 5.4% to +9.40 ± 3.1) CGS 21680-induced relaxation in sEH(-/-). Our data suggest that adenosine-induced relaxation in sEH(-/-) may depend on the upregulation of A(2A) AR, CYP2J, and PPARγ, and the downregulation of A(1) AR and PPARα.

Impact of soluble epoxide hydrolase and epoxyeicosanoids on human health

The presence of epoxyeicosatrienoic acids (EETs) in tissues and their metabolism by soluble epoxide hydrolase (sEH) to 1,2-diols were first reported 30 years ago. However, appreciation of their importance in cell biology and physiology has greatly accelerated over the past decade with the discovery of metabolically stable inhibitors of sEH, the commercial availability of EETs, and the development of analytical methods for the quantification of EETs and their diols. Numerous roles of EETs in regulatory biology now are clear, and the value of sEH inhibition in various animal models of disease has been demonstrated. Here, we review these results and discuss how the pharmacological stabilization of EETs and other natural epoxy-fatty acids could lead to possible disease therapies.

Pharmacokinetics and in vivo potency of soluble epoxide hydrolase inhibitors in cynomolgus monkeys

BACKGROUND AND PURPOSE

Soluble epoxide hydrolase inhibitors (sEHIs) possess anti-inflammatory, antiatherosclerotic, antihypertensive and analgesic properties. The pharmacokinetics (PK) and pharmacodynamics in terms of inhibitory potency of sEHIs were assessed in non-human primates (NHPs). Development of a sEHI for use in NHPs will facilitate investigations on the role of sEH in numerous chronic inflammatory conditions.

EXPERIMENTAL APPROACH

PK parameters of 11 sEHIs in cynomolgus monkeys were determined after oral dosing with 0.3 mg·kg(-1). Their physical properties and inhibitory potency in hepatic cytosol of cynomolgus monkeys were examined. Dose-dependent effects of the two inhibitors 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU) and the related acetyl piperidine derivative, 1-trifluoromethoxyphenyl-3-(1-acetylpiperidin-4-yl) urea (TPAU), on natural blood eicosanoids, were determined.

KEY RESULTS

Among the inhibitors tested, TPPU and two 4-(cyclohexyloxy) benzoic acid urea sEHIs displayed high plasma concentrations (>10 × IC(50)), when dosed orally at 0.3 mg·kg(-1). Although the 4-(cyclohexyloxy) benzoic acid ureas were more potent against monkey sEH than piperidyl ureas (TPAU and TPPU), the latter compounds showed higher plasma concentrations and more drug-like properties. The C(max) increased with dose from 0.3 to 3 mg·kg(-1) for TPPU and from 0.1 to 3 mg·kg(-1) for TPAU, although it was not linear over this range of doses. As an indication of target engagement, ratios of linoleate epoxides to diols increased with TPPU administration.

CONCLUSION AND IMPLICATIONS

Our data indicate that TPPU is suitable for investigating sEH biology and the role of epoxide-containing lipids in modulating inflammatory diseases in NHPs.

Quantitative profiling of oxylipins through comprehensive LC-MS/MS analysis: application in cardiac surgery

Oxylipins, including eicosanoids, affect a broad range of biological processes, such as the initiation and resolution of inflammation. These compounds, also referred to as lipid mediators, are (non-) enzymatically generated by oxidation of polyunsaturated fatty acids such as arachidonic acid (AA). A plethora of lipid mediators exist which makes the development of generic analytical methods challenging. Here we developed a robust and sensitive targeted analysis platform for oxylipins and applied it in a biological setting, using high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) operated in dynamic multiple reaction monitoring (dMRM). Besides the well-described AA metabolites, oxylipins derived from linoleic acid, dihomo-γ-linolenic acid, α-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid were included. Our comprehensive platform allows the quantitative evaluation of approximately 100 oxylipins down to low nanomolar levels. Applicability of the analytical platform was demonstrated by analyzing plasma samples of patients undergoing cardiac surgery. Altered levels of some of the oxylipins, especially in certain monohydroxy fatty acids such as 12-HETE and 12-HEPE, were observed in samples collected before and 24 h after cardiac surgery. These findings indicate that this generic oxylipin profiling platform can be applied broadly to study these highly bioactive compounds in relation to human disease.

Soluble epoxide hydrolase expression in a porcine model of arteriovenous graft stenosis and anti-inflammatory effects of a soluble epoxide hydrolase inhibitor

Synthetic arteriovenous (AV) grafts, placed between an artery and vein, are used for hemodialysis but often fail due to stenosis, typically at the vein-graft anastomosis. This study recorded T lymphocyte and macrophage accumulation at the vein-graft anastomosis, suggesting a role for inflammation in stenosis development. Epoxyeicosatrienoic acids (EETs), products of cytochrome P-450 epoxidation of arachidonic acid, have vasculoprotective and anti-inflammatory effects including inhibition of platelet activation, cell migration, and adhesion. EETs are hydrolyzed by soluble epoxide hydrolase (sEH) to less active diols. The effects of a specific inhibitor of sEH (sEHI) on cytokine release from human monocytes and mouse bone marrow-derived macrophages (BMMΦ) from wild-type (WT) and sEH knockout (KO) animals were investigated. Expression of sEH protein increased over time at the anastomosis as evaluated by immunohistochemistry. Pre-exposure of adherent human monocytes to sEHI (5 μM) significantly inhibited lipopolysaccharide-induced release of monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor-α and enhanced the EET-to-diol ratio. Release of MCP-1 from WT BMMΦ was significantly inhibited but release from sEH KO BMMΦ was not attenuated indicating the specificity of the sEHI. In contrast, sEHI did not inhibit the release of macrophage inflammatory protein-1 or interleukin-6. Nuclear translocation of NF-κB, as assessed by immunocytochemical staining, was not decreased with sEHI in monocytes, but the phosphorylation of JNK was completely abrogated, suggesting this pathway is the target of sEHI effects in monocytes. These results suggest that sEHI may be useful for inhibition of inflammation and subsequently stenosis in AV grafts.

The protective effect of astrocyte-derived 14,15-epoxyeicosatrienoic acid on hydrogen peroxide-induced cell injury in astrocyte-dopaminergic neuronal cell line co-culture

Astrocytes perform several functions that are essential for normal neuronal activity. They play a critical role in neuronal survival during ischemia and other degenerative injuries and also modulate neuronal recovery by influencing neurite outgrowth. In this study, we investigated the neuroprotective effects of astrocyte-derived 14,15-epoxyeicosatrienoic acid (14,15-EET), metabolite of arachidonic acid by cytochrome P450 epoxygenases (CYP), against oxidative stress induced by hydrogen peroxide (H(2)O(2)). We found that dopaminergic neuronal cells (N27 cell line) stimulated with two different doses of H(2)O(2) (0.1 and 1mM) for 1h showed decreased cell viability compared to the control group, while astrocytes showed less cell death after stimulation with the same doses of H(2)O(2) for 1h. Dopaminergic neuronal cells (N27 cell line) pretreated with different doses of 14,15-EET (0.1-30 μM, 30 min) before H(2)O(2) stimulation also showed increased cell viability. Furthermore, pre-treatment of the co-cultured cells with 12-(3-adamantan-1-yl-ureido)-dodecanoic acid, an inhibitor of the EET metabolizing enzyme, soluble epoxide hydrolase (sEH), before H(2)O(2) stimulation (1mM, for 1h) increased cell viability. It also increased the endogenous level of 14,15-EET in the media compared to control group. However, pretreatment with the CYP epoxygenase inhibitor miconazole (1-20 μM, 1h) before H(2)O(2) (1mM, 1h) stimulation showed decreased cell viability. Our data suggest that 14,15-EET which is released from astrocytes, enhances cell viability against oxidant-induced injury. Further understanding of the mechanism of 14,15-EET-mediated protection in dopaminergic neurons is imperative, as it could lead to novel therapeutic approaches for treating CNS neuropathologies, such as Parkinson's disease.

Role of epoxide hydrolases in lipid metabolism

Epoxide hydrolases (EH), enzymes present in all living organisms, transform epoxide-containing lipids to 1,2-diols by the addition of a molecule of water. Many of these oxygenated lipid substrates have potent biological activities: host defense, control of development, regulation of blood pressure, inflammation, and pain. In general, the bioactivity of these natural epoxides is significantly reduced upon metabolism to diols. Thus, through the regulation of the titer of lipid epoxides, EHs have important and diverse biological roles with profound effects on the physiological state of the host organism. This review will discuss the biological activity of key lipid epoxides in mammals. In addition, the use of EH specific inhibitors will be highlighted as possible therapeutic disease interventions.

A potent soluble epoxide hydrolase inhibitor, t-AUCB, acts through PPARγ to modulate the function of endothelial progenitor cells from patients with acute myocardial infarction

BACKGROUND

Epoxyeicosatrienoic acids (EETs) are natural angiogenic mediators regulated by soluble epoxide hydrolase (sEH). Inhibitors of sEH can stabilize EETs levels and were reported to reduce atherosclerosis and inhibit myocardial infarction in animal models. In this work, we investigated whether increasing EETs with the sEH inhibitor t-AUCB would increase angiogenesis related function in endothelial progenitor cells (EPCs) from patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

EPCs were isolated from 50 AMI patients and 50 healthy subjects (control). EPCs were treated with different concentrations of t-AUCB for 24h with or without peroxisome proliferator activated receptor γ (PPARγ) inhibitor GW9662. Migration of EPCs was assayed in trans-well chambers. Angiogenesis assays were performed using a Matrigel-Matrix in vitro model. The expression of vascular endothelial growth factor (VEGF), hypoxia-inducible factor 1α (HIF-1α) mRNA and protein in EPCs was measured by real-time PCR or Western blot, respectively. Also, the concentration of EETs in the culture supernatant was detected by ELISA. The activity of EPCs in the AMI patient group was reduced compared to healthy controls. Whereas increasing EET levels with t-AUCB promoted a dose dependent angiogenesis and migration in EPCs from AMI patients. Additionally, the t-AUCB dose dependently increased the expression of the angiogenic factors VEGF and HIF-α. Lastly, we provide evidence that these effects were PPARγ dependent.

CONCLUSION

The results demonstrate that the sEH inhibitor positively modulated the functions of EPCs in patients with AMI through the EETs-PPARγ pathway. The present study suggests the potential utility of sEHi in the therapy of ischemic heart disease.

Reduction of inflammatory bowel disease-induced tumor development in IL-10 knockout mice with soluble epoxide hydrolase gene deficiency

Soluble epoxide hydrolase (sEH) quickly inactivates anti-inflammatory epoxyeicosatrienoic acids (EETs) by converting them to dihydroxyeicosatrienoic acids (DHETs). Inhibition of sEH has shown effects against inflammation, but little is studied about the role of sEH in inflammatory bowel disease (IBD) and its induced carcinogenesis. In the present study, the effect of sEH gene deficiency on the development of IBD-induced tumor development was determined in IL-10 knockout mice combined with sEH gene deficiency. Tumor development in the bowel was examined at the age of 25 wk for male mice and 35 wk for female mice. Compared to IL-10(-/-) mice, sEH (-/-)/IL-10(-/-) mice exhibited a significant decrease of tumor multiplicity (2 ± 0.9 tumors/mouse vs. 1 ± 0.3 tumors/mouse) and tumor size (344.55 ± 71.73 mm³ vs. 126.94 ± 23.18 mm³), as well as a marked decrease of precancerous dysplasia. The significantly lower inflammatory scores were further observed in the bowel in sEH(-/-)/IL-10(-/-) mice as compared to IL-10(-/-) mice, including parameters of inflammation-involved area (0.70 ± 0.16 vs. 1.4 ± 0.18), inflammation cell infiltration (1.55 ± 0.35 vs. 2.15 ± 0.18), and epithelial hyperplasia (0.95 ± 0.21 vs. 1.45 ± 0.18), as well as larger ulcer formation. qPCR and Western blotting assays demonstrated a significant downregulation of cytokines/chemokines (TNF-α, MCP-1, and IL-12, 17, and 23) and NF-κB signals. Eicosanoid acid metabolic profiling revealed a significant increase of ratios of EETs to DHETs and EpOMEs to DiOMEs. These results indicate that sEH plays an important role in IBD and its-induced carcinogenesis and could serve as a highly potential target of chemoprevention and treatment for IBD.

Epoxides and soluble epoxide hydrolase in cardiovascular physiology

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites that importantly contribute to vascular and cardiac physiology. The contribution of EETs to vascular and cardiac function is further influenced by soluble epoxide hydrolase (sEH) that degrades EETs to diols. Vascular actions of EETs include dilation and angiogenesis. EETs also decrease inflammation and platelet aggregation and in general act to maintain vascular homeostasis. Myocyte contraction and increased coronary blood flow are the two primary EET actions in the heart. EET cell signaling mechanisms are tissue and organ specific and provide significant evidence for the existence of EET receptors. Additionally, pharmacological and genetic manipulations of EETs and sEH have demonstrated a contribution for this metabolic pathway to cardiovascular diseases. Given the impact of EETs to cardiovascular physiology, there is emerging evidence that development of EET-based therapeutics will be beneficial for cardiovascular diseases.

Role of soluble epoxide hydrolase phosphatase activity in the metabolism of lysophosphatidic acids

The EPXH2 gene encodes for the soluble epoxide hydrolase (sEH), which has two distinct enzyme activities: epoxide hydrolase (Cterm-EH) and phosphatase (Nterm-phos). The Cterm-EH is involved in the metabolism of epoxides from arachidonic acid and other unsaturated fatty acids, endogenous chemical mediators that play important roles in blood pressure regulation, cell growth, inflammation and pain. While recent findings suggested complementary biological roles for Nterm-phos, its mode of action is not well understood. Herein, we demonstrate that lysophosphatidic acids are excellent substrates for Nterm-phos. We also showed that sEH phosphatase activity represents a significant (20-60%) part of LPA cellular hydrolysis, especially in the cytosol. This possible role of sEH on LPA hydrolysis could explain some of the biology previously associated with the Nterm-phos. These findings also underline possible cellular mechanisms by which both activities of sEH (EH and phosphatase) may have complementary or opposite roles.

Investigation of a possible relationship between EPHX1 gene polymorphisms and colorectal cancer in Turkish society

Metabolism of chemical carcinogens, including their activation and detoxification, plays a key role in carcinogenesis. Microsomal epoxide hydrolase (EPHX1) has an important role in the metabolism of polycyclic aromatic hydrocarbons and detoxification of procarcinogens. The aim of this study was to investigate the association between colorectal cancer (CRC) development and EPHX1 gene polymorphisms. We investigated the polymorphisms in exon 3 (T>C, Tyr113His) and exon 4 (A>G, His139Arg) of the EPHX1 gene in 68 CRC patients and 116 controls by polymerase chain reaction-restriction fragment length polymorphism. The frequencies of the Try113Try, Try113His, and His113His for EPHX1 exon 3 were 37.9%, 55.2%, and 6.9% in controls and 39.7%, 42.6%, and 17.6% in CRC patients, respectively. Frequencies of EPHX1 exon 4 genotypes were 62.1% His139His, 37.9% His139Arg, and 0% Arg139Arg in the control group and 76.5% His139His, 22.1% His139Arg, and 1.5% Arg139Arg in the patient group. Individuals carrying the EPHX1 exon 3 His113His genotype had a 2.5-fold increased risk (p=0.024), and those carrying the EPHX1 exon 4 His139Arg genotype had decreased risk of CRC compared with controls (p=0.019). Even though exon 3 Tyr113His and exon 4 His139Arg polymorphisms for EPHX1 gene appear to be important factors for CRC risk, further investigations with larger study groups are needed to fully elucidate the role of these polymorphisms in the development of CRC.

Reno-protective mechanisms of epoxyeicosatrienoic acids in cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, and it is well known that end-stage renal disease (ESRD) is a profound consequence of the progression of CVD. Present treatments only slow CVD progression to ESRD, and it is imperative that new therapeutic strategies are developed to prevent the incidence of ESRD. Because epoxyeicosatrienoic acids (EETs) have been shown to elicit reno-protective effects in hypertensive animal models, the current review will focus on addressing the reno-protective mechanisms of EETs in CVD. The cytochrome P-450 epoxygenase catalyzes the oxidation of arachidonic acid to EETs. EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs) with vasodilatory, anti-inflammatory, antihypertensive, and antiplatelet aggregation properties. EETs also have profound effects on vascular migration and proliferation and promote angiogenesis. The progression of CVD has been linked to decreased EETs levels, leading to the concept that EETs should be therapeutically targeted to prevent end-organ damage associated with CVD. However, EETs are quickly degraded by the enzyme soluble epoxide hydrolase (sEH) to their less active diols, dihydroxyeicosatrienoic acids (DHETs). As such, one way to increase EETs level is to inhibit their degradation to DHETs by using sEH inhibitors. Inhibition of sEH has been shown to effectively reduce blood pressure and organ damage in experimental models of CVD. Another approach to target EETs is to develop EET analogs with improved solubility and resistance to auto-oxidation and metabolism by sEH. For example, stable ether EET analogs dilate afferent arterioles and lower blood pressure in hypertensive rodent animal models. EET agonists also improve insulin signaling and vascular function in animal models of metabolic syndrome.

Surprising unreactivity of cholesterol-5,6-epoxides towards nucleophiles

We recently established that drugs used for the treatment and the prophylaxis of breast cancers, such as tamoxifen, were potent inhibitors of cholesterol-5,6-epoxide hydrolase (ChEH), which led to the accumulation of 5,6α-epoxy-cholesterol (5,6α-EC) and 5,6β-epoxy-cholesterol (5,6β-EC). This could be considered a paradox because epoxides are known as alkylating agents with putative carcinogenic properties. We report here that, as opposed to the carcinogen styrene-oxide, neither of the ECs reacted spontaneously with nucleophiles. Under catalytic conditions, 5,6β-EC remains unreactive whereas 5,6α-EC gives cholestan-3β,5α-diol-6β-substituted compounds. These data showed that 5,6-ECs are stable epoxides and unreactive toward nucleophiles in the absence of a catalyst, which contrasts with the well-known reactivity of aromatic and aliphatic epoxides. These data rule out 5,6-EC acting as spontaneous alkylating agents. In addition, these data support the existence of a stereoselective metabolism of 5,6α-EC.

Development of monoclonal antibodies to human microsomal epoxide hydrolase and analysis of "preneoplastic antigen"-like molecules

Microsomal epoxide hydrolase (mEH) is a drug metabolizing enzyme which resides on the endoplasmic reticulum (ER) membrane and catalyzes the hydration of reactive epoxide intermediates that are formed by cytochrome P450s. mEH is also thought to have a role in bile acid transport on the plasma membrane of hepatocytes. It is speculated that efficient execution of such multiple functions is secured by its orientation and association with cytochrome P450 enzymes on the ER membrane and formation of a multiple transport system on the plasma membrane. In certain disease status, mEH loses its association with the membrane and can be detected as distinct antigens in the cytosol of preneoplastic foci of liver (preneoplastic antigen), in the serum in association with hepatitis C virus infection (AN antigen), or in some brain tumors. To analyze the antigenic structures of mEH in physiological and pathological conditions, we developed monoclonal antibodies against different portions of mEH. Five different kinds of antibodies were obtained: three, anti-N-terminal portions; one anti-C-terminal; and one, anti-conformational epitope. By combining these antibodies, we developed antigen detection methods which are specific to either the membrane-bound form or the linearized form of mEH. These methods detected mEH in the culture medium released from a hepatocellular carcinoma cell line and a glioblastoma cell line, which was found to be a multimolecular complex with a unique antigenic structure different from that of the membrane-bound form of mEH. These antibodies and antigen detection methods may be useful to study pathological changes of mEH in various human diseases.

Monoclonal antibodies reveal multiple forms of expression of human microsomal epoxide hydrolase

In a previous study, we developed five kinds of monoclonal antibodies against different portions of human mEH: three, anti-N-terminal; one, anti-C-terminal; one, anti-conformational epitope. Using them, we stained the intact and the permeabilized human cells of various kinds and performed flow cytometric analysis. Primary hepatocytes and peripheral blood mononuclear cells (PBMC) showed remarkable differences. On the surface, hepatocytes exhibited 4 out of 5 epitopes whereas PBMC did not show any of the epitopes. mEH was detected inside both cell types, but the most prominent expression was observed for the conformational epitope in the hepatocytes and the two N-terminal epitopes in PBMC. These differences were also observed between hepatocyte-derived cell lines and mononuclear cell-derived cell lines. In addition, among each group, there were several differences which may be related to the cultivation, the degree of differentiation, or the original cell subsets. We also noted that two glioblastoma cell lines reveal marked expression of the conformational epitope on the surface which seemed to correlate with the brain tumor-associated antigen reported elsewhere. Several cell lines also underwent selective permeabilization before flow cytometric analysis, and we noticed that the topological orientation of mEH on the ER membrane in those cells was in accordance with the previous report. However, the orientation on the cell surface was inconsistent with the report and had a great variation between the cells. These findings show the multiple mode of expression of mEH which may be possibly related to the multiple roles that mEH plays in different cells.

The increasing role of QM/MM in drug discovery

Since its first appearance in 1976, the quantum mechanics/molecular mechanics (QM/MM) approach has mostly been used to study the chemical reactions of enzymes, which are frequently the target of drug discovery programs. In principle, a detailed understanding of the enzymatic mechanism should help researchers to design a potent enzyme inhibitor or new drug. However, QM/MM has not yet had a widespread impact on structure-based drug design. This is mostly due to its high computational cost. We expect this to change with the recent and extraordinary increases in computational power, and with the availability of more efficient algorithms for QM/MM calculations. Here, we report on some representative examples of QM/MM studies, including our own research, of pharmaceutically relevant enzymes, such as ribonuclease H and fatty acid amide hydrolase (FAAH). We aim to show how QM/MM has traditionally been used to study enzymatic catalysis. In this regard, we discuss its potential to become a routinely used drug design tool. To support this, we also discuss selected computational studies where QM/MM insights have been helpful in improving the potency of covalent inhibitors of FAAH.