Attenuation of tobacco smoke-induced lung inflammation by treatment with a soluble epoxide hydrolase inhibitor

Ingestion of the epoxide hydrolase inhibitor AUDA modulates immune responses of the mosquito, Culex quinquefasciatus during blood feeding

Epoxide hydrolases (EHs) are enzymes that play roles in metabolizing xenobiotic epoxides from the environment, and in regulating lipid signaling molecules, such as juvenile hormones in insects and epoxy fatty acids in mammals. In this study we fed mosquitoes with an epoxide hydrolase inhibitor AUDA during artificial blood feeding, and we found the inhibitor increased the concentration of epoxy fatty acids in the midgut of female mosquitoes. We also observed ingestion of AUDA triggered early expression of defensin A, cecropin A and cecropin B2 at 6 h after blood feeding. The expression of cecropin B1 and gambicin were not changed more than two fold compared to controls. The changes in gene expression were transient possibly because more than 99% of the inhibitor was metabolized or excreted at 42 h after being ingested. The ingestion of AUDA also affected the growth of bacteria colonizing in the midgut, but did not affect mosquito longevity, fecundity and fertility in our laboratory conditions. When spiked into the blood, EpOMEs and DiHOMEs were as effective as the inhibitor AUDA in reducing the bacterial load in the midgut, while EETs rescued the effects of AUDA. Our data suggest that epoxy fatty acids from host blood are immune response regulators metabolized by epoxide hydrolases in the midgut of female mosquitoes, inhibition of which causes transient changes in immune responses, and affects growth of microbes in the midgut.

Possible role of Epoxyeicosatrienoic acid in prevention of oxidative stress mediated neuroinflammation in Parkinson disorders

Parkinson's disease (PD) is a multifactorial neurodegenerative disease involving oxidative stress, neuroinflammation and apoptosis. Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites and they play a role in cytoprotection by modulating various cell signaling pathways. This cytoprotective role of EETs are well established in cerebral stroke, cardiac failure, and hypertension, and it is due to their ability to attenuate oxidative stress, endoplasmic reticulum stress, inflammation, caspase activation and apoptosis. The actions of EETs in brain closely parallel the effects which is observed in the peripheral tissues. Since many of these effects could potentially contribute to neuroprotection, EETs are, therefore, one of the potential therapeutic candidates in PD. Therefore, by increasing the half life of endogenous EETs in vivo via inhibition of sEH, its metabolizing enzyme can, therefore, constitutes an important therapeutic strategy in PD.

Pharmacokinetics, pharmacodynamics and adverse event profile of GSK2256294, a novel soluble epoxide hydrolase inhibitor

AIMS

Endothelial-derived epoxyeicosatrienoic acids may regulate vascular tone and are metabolized by soluble epoxide hydrolase enzymes (sEH). GSK2256294 is a potent and selective sEH inhibitor that was tested in two phase I studies.

METHODS

Single escalating doses of GSK2256294 2-20 mg or placebo were administered in a randomized crossover design to healthy male subjects or obese smokers. Once daily doses of 6 or 18 mg or placebo were administered for 14 days to obese smokers. Data were collected on safety, pharmacokinetics, sEH enzyme inhibition and blood biomarkers. Single doses of GSK2256294 10 mg were also administered to healthy younger males or healthy elderly males and females with and without food. Data on safety, pharmacokinetics and biliary metabolites were collected.

RESULTS

GSK2256294 was well-tolerated with no serious adverse events (AEs) attributable to the drug. The most frequent AEs were headache and contact dermatitis. Plasma concentrations of GSK2256294 increased with single doses, with a half-life averaging 25-43 h. There was no significant effect of age, food or gender on pharmacokinetic parameters. Inhibition of sEH enzyme activity was dose-dependent, from an average of 41.9% on 2 mg (95% confidence interval [CI] -51.8, 77.7) to 99.8% on 20 mg (95% CI 99.3, 100.0) and sustained for up to 24 h. There were no significant changes in serum VEGF or plasma fibrinogen.

CONCLUSIONS

GSK2256294 was well-tolerated and demonstrated sustained inhibition of sEH enzyme activity. These data support further investigation in patients with endothelial dysfunction or abnormal tissue repair, such as diabetes, wound healing or COPD.

A multimodal disease modifying approach to treat neuropathic pain--inhibition of soluble epoxide hydrolase (sEH)

Both neuronal and non-neuronal mechanisms have been proposed to contribute to neuropathic pain (NP). All currently approved treatments for NP modulate neuronal targets and provide only symptomatic relief. Here we review evidence that inhibition of soluble epoxide hydrolase (sEH), the enzyme that degrades epoxyeicosatrienoic acids (EETs), has potential to be a multimodal, disease modifying approach to treat NP: (1) EET actions involve both endogenous opioid system and the GABAergic systems thus provide superior pain relief compared to morphine or gabapentin, (2) EETs are directly anti-inflammatory and inhibit expression of inflammatory cytokines and adhesion molecules thus can prevent continued nerve damage; and (3) EETs promote nerve regeneration in cultured neurons. Thus, an sEH inhibitor will not only provide effective pain relief, but would also block further nerve damage and promote healing.

The 2014 Bernard B. Brodie award lecture-epoxide hydrolases: drug metabolism to therapeutics for chronic pain

Dr. Bernard Brodie's legacy is built on fundamental discoveries in pharmacology and drug metabolism that were then translated to the clinic to improve patient care. Similarly, the development of a novel class of therapeutics termed the soluble epoxide hydrolase (sEH) inhibitors was originally spurred by fundamental research exploring the biochemistry and physiology of the sEH. Here, we present an overview of the history and current state of research on epoxide hydrolases, specifically focusing on sEHs. In doing so, we start with the translational project studying the metabolism of the insect juvenile hormone mimic R-20458 [(E)-6,7-epoxy-1-(4-ethylphenoxy)-3,7-dimethyl-2-octene], which led to the identification of the mammalian sEH. Further investigation of this enzyme and its substrates, including the epoxyeicosatrienoic acids, led to insight into mechanisms of inflammation, chronic and neuropathic pain, angiogenesis, and other physiologic processes. This basic knowledge in turn led to the development of potent inhibitors of the sEH that are promising therapeutics for pain, hypertension, chronic obstructive pulmonary disorder, arthritis, and other disorders.

Bioactive lipid profiling reveals drug target engagement of a soluble epoxide hydrolase inhibitor in a murine model of tobacco smoke exposure

The inflammatory process underlying chronic obstructive pulmonary disease (COPD) may be caused by tobacco smoke (TS) exposure. Previous studies show that epoxyeicosatrienoic acids (EETs) possess promising anti-inflammatory properties, therefore stabilization of EETs and other fatty acid epoxides through inhibition of soluble epoxide hydrolase (sEH) was investigated in mouse models of acute and sub-chronic inflammation caused by TS exposure. During the entire TS exposure, the potent sEH inhibitor 1-(1-methylsulfonyl-piperidin-4-yl)-3-(4-trifluoromethoxy-phenyl)-urea (TUPS) was given via drinking water. To assess drug target engagement of TUPS, a tandem mass spectrometry method was used for bioactive lipid profiling of a broad range of fatty acid metabolites, including EETs, and their corresponding diols (DHETs) derived from arachidonic acid, as well as epoxides and diols derived from other fatty acids. Several, but not all, plasma epoxide/diol ratios increased in mice treated with sEH inhibitor, compared to non-treated mice suggesting a wider role for sEH involving more fatty acid precursors besides arachidonic acid. This study supports qualitative use of epoxide/diol ratios explored by bioactive lipid profiling to indicate drug target engagement in mouse models of TS exposure relevant to COPD, which may have ramifications for future therapeutic interventions of sEH.

Macrophage epoxygenase determines a profibrotic transcriptome signature

Epoxygenases belong to the cytochrome P450 family. They generate epoxyeicosatrienoic acids, which are known to have anti-inflammatory effects, but little is known about their role in macrophage function. By high-throughput sequencing of RNA in primary macrophages derived from rodents and humans, we establish the relative expression of epoxygenases in these cells. Zinc-finger nuclease-mediated targeted gene deletion of the major rat macrophage epoxygenase Cyp2j4 (ortholog of human CYP2J2) resulted in reduced epoxyeicosatrienoic acid synthesis. Cyp2j4(-/-) macrophages have relatively increased peroxisome proliferator-activated receptor-γ levels and show a profibrotic transcriptome, displaying overexpression of a specific subset of genes (260 transcripts) primarily involved in extracellular matrix, with fibronectin being the most abundantly expressed transcript. Fibronectin expression is under the control of epoxygenase activity in human and rat primary macrophages. In keeping with the in vitro findings, Cyp2j4(-/-) rats show upregulation of type I collagen following unilateral ureter obstruction of the kidney, and quantitative proteomics analysis (liquid chromatography-tandem mass spectrometry) showed increased renal type I collagen and fibronectin protein abundance resulting from experimentally induced crescentic glomerulonephritis in these rats. Taken together, these results identify the rat epoxygenase Cyp2j4 as a determinant of a profibrotic macrophage transcriptome that could have implications in various inflammatory conditions, depending on macrophage function.

Soluble epoxide hydrolase inhibitor attenuates inflammation and airway hyperresponsiveness in mice

Control of airway inflammation is critical in asthma treatment. Soluble epoxide hydrolase (sEH) has recently been demonstrated as a novel therapeutic target for treating inflammation, including lung inflammation. We hypothesized that pharmacological inhibition of sEH can modulate the inflammatory response in a murine ovalbumin (OVA) model of asthma. BALB/c mice were sensitized and exposed to OVA over 6 weeks. A sEH inhibitor (sEHI) was administered for 2 weeks. Respiratory system compliance, resistance, and forced exhaled nitric oxide were measured. Lung lavage cell counts were performed, and selected cytokines and chemokines in the lung lavage fluid were measured. A LC/MS/MS method was used to measure 87 regulatory lipids mediators in plasma, lung tissue homogenates, and lung lavage fluid. The pharmacological inhibition of sEH increased concentrations of the antiinflammatory epoxy eicosatrienoic acids and simultaneously decreased the concentrations of the proinflammatory dihydroxyeicosatrienoic acids and dihydroxyoctadecenoic acids. All monitored inflammatory markers, including FeNO levels, and total cell and eosinophil numbers in the lung lavage of OVA-exposed mice were reduced by sEHI. The type 2 T helper cell (Th2) cytokines (IL-4, IL-5) and chemokines (Eotaxin and RANTES) were dramatically reduced after sEHI administration. Resistance and dynamic lung compliance were also improved by sEHI. We demonstrated that sEHI administration attenuates allergic airway inflammation and airway responsiveness in a murine model. sEHI may have potential as a novel therapeutic strategy for allergic asthma.

Epoxyeicosatrienoic acids attenuate cigarette smoke extract-induced interleukin-8 production in bronchial epithelial cells

In response to endothelial cell activation, arachidonic acid can be converted by cytochrome P450 (CYP) epoxygenases to epoxyeicosatrienoic acids (EETs), which have potent vasodilator and anti-inflammatory properties. In this study, we investigated the effects of exogenous EETs on cigarette smoke extract (CSE)-induced inflammation in human bronchial epithelial cells (NCI-H292). We found that CSE inhibited the expression of CYP2C8 and mildly stimulated the expression of epoxide hydrolase 2 (EPHX2) but did not change the expression of CYP2J2. Treatment with 11,12-EET or 14,15-EET attenuated the CSE-induced release of interleukin (IL)-8 by inhibiting the phosphorylation of p38 mitogen-activated protein kinases (MAPKs). Our results demonstrated that CSE may reduce the anti-inflammatory ability of epithelial cells themselves by lowering the EET level. EETs from pulmonary epithelial cells may play a critical protective role on epithelial cell injury.

Lipoxin generation is related to soluble epoxide hydrolase activity in severe asthma

RATIONALE

Severe asthma is characterized by airway inflammatory responses associated with aberrant metabolism of arachidonic acid. Lipoxins (LX) are arachidonate-derived pro-resolving mediators that are decreased in severe asthma, yet mechanisms for defective LX biosynthesis and a means to increase LXs in severe asthma remain to be established.

OBJECTIVES

To determine if oxidative stress and soluble epoxide hydrolase (sEH) activity are linked to decreased LX biosynthesis in severe asthma.

METHODS

Aliquots of blood, sputum, and bronchoalveolar lavage fluid were obtained from asthma subjects for mediator determination. Select samples were exposed to t-butyl-hydroperoxide or sEH inhibitor (sEHI) before activation. Peripheral blood leukocyte-platelet aggregates were monitored by flow cytometry, and bronchial contraction was determined with cytokine-treated human lung sections.

MEASUREMENTS AND MAIN RESULTS

8-Isoprostane levels in sputum supernatants were inversely related to LXA4 in severe asthma (r = -0.55; P = 0.03) and t-butyl-hydroperoxide decreased LXA4 and 15-epi-LXA4 biosynthesis by peripheral blood leukocytes. LXA4 and 15-epi-LXA4 levels were inversely related to sEH activity in sputum supernatants and sEHIs significantly increased 14,15-epoxy-eicosatrienoic acid and 15-epi-LXA4 generation by severe asthma whole blood and bronchoalveolar lavage fluid cells. The abundance of peripheral blood leukocyte-platelet aggregates was related to asthma severity. In a concentration-dependent manner, LXs significantly inhibited platelet-activating factor-induced increases in leukocyte-platelet aggregates (70.8% inhibition [LXA4 100 nM], 78.3% inhibition [15-epi-LXA4 100 nM]) and 15-epi-LXA4 markedly inhibited tumor necrosis factor-α-induced increases in bronchial contraction.

CONCLUSIONS

LX levels were decreased by oxidative stress and sEH activity. Inhibitors of sEH increased LXs that mediated antiphlogistic actions, suggesting a new therapeutic approach for severe asthma. Clinical trial registered with www.clinicaltrials.gov (NCT 00595114).

Epoxyeicosanoids suppress osteoclastogenesis and prevent ovariectomy-induced bone loss

Epoxyeicosatrienoic acids (EETs) are products of arachidonic acid metabolism catalyzed by cytochrome P450 epoxygenases. These small molecules are autocrine and paracrine lipid mediators with important roles in inflammation, cardiovascular function, and angiogenesis. Recent evidence has highlighted EETs as potent promoters of organ regeneration and malignant metastasis. We speculated that EETs might impact osteoclastogenesis and bone loss. Using both in vitro and in vivo studies, we observed that EETs significantly attenuated bone loss and inhibited osteoclast formation and activity, which were associated with a decreased receptor activator of NF-κB ligand (RANKL):osteoprotegerin ratio and serum levels of TNF-α and IL-1β. At the molecular level, EETs abrogated RANKL-induced activation of NF-κB, activator protein-1 (AP-1), and MAPKs, including ERK and JNK, but not p38, during osteoclast formation. EETs also prevented the production of reactive oxygen species (ROS) following RANKL stimulation. As a result, EETs suppressed osteoclast-specific gene expression, including tartrate resistant acid phosphatase (TRAP), cathepsin K (CK), matrix metalloproteinase (MMP)-9, and receptor activator of NF-κB (RANK). In conclusion, our findings demonstrate that EETs inhibit osteoclastogenesis through modulation of multiple pathways both upstream and downstream of RANKL signaling. The administration or stabilized endogenous levels of EETs could represent a novel therapeutic strategy for osteoclast-related disorders, such as rheumatoid arthritis and postmenopausal osteoporosis.

The role of epoxide hydrolases in health and disease

Epoxide hydrolases (EH) are ubiquitously expressed in all living organisms and in almost all organs and tissues. They are mainly subdivided into microsomal and soluble EH and catalyze the hydration of epoxides, three-membered-cyclic ethers, to their corresponding dihydrodiols. Owning to the high chemical reactivity of xenobiotic epoxides, microsomal EH is considered protective enzyme against mutagenic and carcinogenic initiation. Nevertheless, several endogenously produced epoxides of fatty acids function as important regulatory mediators. By mediating the formation of cytotoxic dihydrodiol fatty acids on the expense of cytoprotective epoxides of fatty acids, soluble EH is considered to have cytotoxic activity. Indeed, the attenuation of microsomal EH, achieved by chemical inhibitors or preexists due to specific genetic polymorphisms, is linked to the aggravation of the toxicity of xenobiotics, as well as the risk of cancer and inflammatory diseases, whereas soluble EH inhibition has been emerged as a promising intervention against several diseases, most importantly cardiovascular, lung and metabolic diseases. However, there is reportedly a significant overlap in substrate selectivity between microsomal and soluble EH. In addition, microsomal and soluble EH were found to have the same catalytic triad and identical molecular mechanism. Consequently, the physiological functions of microsomal and soluble EH are also overlapped. Thus, studying the biological effects of microsomal or soluble EH alterations needs to include the effects on both the metabolism of reactive metabolites, as well as epoxides of fatty acids. This review focuses on the multifaceted role of EH in the metabolism of xenobiotic and endogenous epoxides and the impact of EH modulations.

EETs alleviate ox-LDL-induced inflammation by inhibiting LOX-1 receptor expression in rat pulmonary arterial endothelial cells

Oxidized low-density lipoprotein (Ox-LDL) is associated with atherosclerotic events through the modulation of arachidonic acid (AA) metabolism and activation of inflammatory signaling. Cytochrome P450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) mitigate inflammation through nuclear factor-κB (NF-κB). In this study, we explored the effects and mechanisms of exogenous EETs on the ox-LDL-induced inflammation of pulmonary artery endothelial cells (PAECs), which were cultured from rat pulmonary arteries. We determined that pre-treatment with 11,12-EET or 14,15-EET attenuated the ox-LDL-induced expression and release of intercellular adhesion molecule-1 (ICAM-1), E-selectin, and monocyte chemoattractant protein-1 (MCP-1) in a concentration-dependent manner. In addition, the ox-LDL-induced expression of CYP2J4 was upregulated by 11,12-EET and 14,15-EET (1μM). Furthermore, the endothelial receptor of lectin-like oxidized low-density lipoprotein (LOX-1) was downregulated in PAECs treated with EETs. The inflammatory responses evoked by ox-LDL (100μg/mL) were blocked by pharmacological inhibitors of Erk1/2 mitogen-activated protein kinase (MAPK) (U0126), p38 MAPK (SB203580), and NF-κB (PDTC). In addition, we confirmed that 11,12-EET suppresses phosphorylation of p38, degradation of IκBα, and activation of NF-κB (p65), whereas 14,15-EET can significantly suppress the phosphorylation of p38 and Erk1/2. Our results indicate that EETs exert beneficial effects on ox-LDL-induced inflammation primarily through the inhibition of LOX-1 receptor upregulation, MAPK phosphorylation, and NF-κB activation and through the upregulation of CYP2J4 expression. This study helps focus the current understanding of the contribution of EETs to the regulation of the inflammation of pulmonary vascular endothelial cells. Furthermore, the therapeutic potential of targeting the EET pathway in pulmonary vascular disease will be highlighted.

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.

Role of cytochrome P450-mediated arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

A plethora of studies have demonstrated the expression of cytochrome P450 (CYP) and soluble epoxide hydrolase (sEH) enzymes in the heart and other cardiovascular tissues. In addition, the expression of these enzymes is altered during several cardiovascular diseases (CVDs), including cardiac hypertrophy (CH). The alteration in CYP and sEH expression results in derailed CYP-mediated arachidonic acid (AA) metabolism. In animal models of CH, it has been reported that there is an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and a decrease in epoxyeicosatrienoic acids (EETs). Further, inhibiting 20-HETE production by CYP ω-hydroxylase inhibitors and increasing EET stability by sEH inhibitors have been proven to protect against CH as well as other CVDs. Therefore, CYP-mediated AA metabolites 20-HETE and EETs are potential key players in the pathogenesis of CH. Some studies have investigated the molecular mechanisms by which these metabolites mediate their effects on cardiomyocytes and vasculature leading to pathological CH. Activation of several intracellular signaling cascades, such as nuclear factor of activated T cells, nuclear factor kappa B, mitogen-activated protein kinases, Rho-kinases, Gp130/signal transducer and activator of transcription, extracellular matrix degradation, apoptotic cascades, inflammatory cytokines, and oxidative stress, has been linked to the pathogenesis of CH. In this review, we discuss how 20-HETE and EETs can affect these signaling pathways to result in, or protect from, CH, respectively. However, further understanding of these metabolites and their effects on intracellular cascades will be required to assess their potential translation to therapeutic approaches for the prevention and/or treatment of CH and heart failure.

Simvastatin inhibits smoke-induced airway epithelial injury: implications for COPD therapy

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death. The statin drugs may have therapeutic potential in respiratory diseases such as COPD, but whether they prevent bronchial epithelial injury is unknown. We hypothesised that simvastatin attenuates acute tobacco smoke-induced neutrophilic lung inflammation and airway epithelial injury. Spontaneously hypertensive rats were given simvastatin (20 mg·kg(-1) i.p.) daily for either 7 days prior to tobacco smoke exposure and during 3 days of smoke exposure, or only during tobacco smoke exposure. Pretreatment with simvastatin prior to and continued throughout smoke exposure reduced the total influx of leukocytes, neutrophils and macrophages into the lung and airways. Simvastatin attenuated tobacco smoke-induced cellular infiltration into lung parenchymal and airway subepithelial and interstitial spaces. 1 week of simvastatin pretreatment almost completely prevented smoke-induced denudation of the airway epithelial layer, while simvastatin given only concurrently with the smoke exposure had no effect. Simvastatin may be a novel adjunctive therapy for smoke-induced lung diseases, such as COPD. Given the need for statin pretreatment there may be a critical process of conditioning that is necessary for statins' anti-inflammatory effects. Future work is needed to elucidate the mechanisms of this statin protective effect.

Tobacco smoke induced COPD/emphysema in the animal model-are we all on the same page?

Chronic Obstructive Pulmonary Disease (COPD) is one of the foremost causes of death worldwide. It is primarily caused by tobacco smoke, making it an easily preventable disease, but facilitated by genetic α-1 antitrypsin deficiency. In addition to active smokers, health problems also occur in people involuntarily exposed to second hand smoke (SHS). Currently, the relationship between SHS and COPD is not well established. Knowledge of pathogenic mechanisms is limited, thereby halting the advancement of new treatments for this socially and economically detrimental disease. Here, we attempt to summarize tobacco smoke studies undertaken in animal models, applying both mainstream (direct, nose only) and side stream (indirect, whole body) smoke exposures. This overview of 155 studies compares cellular and molecular mechanisms as well as proteolytic, inflammatory, and vasoreactive responses underlying COPD development. This is a difficult task, as listing of exposure parameters is limited for most experiments. We show that both mainstream and SHS studies largely present similar inflammatory cell populations dominated by macrophages as well as elevated chemokine/cytokine levels, such as TNF-α. Additionally, SHS, like mainstream smoke, has been shown to cause vascular remodeling and neutrophil elastase-mediated proteolytic matrix breakdown with failure to repair. Disease mechanisms and therapeutic interventions appear to coincide in both exposure scenarios. One of the more widely applied interventions, the anti-oxidant therapy, is successful for both mainstream and SHS. The comparison of direct with indirect smoke exposure studies in this review emphasizes that, even though there are many overlapping pathways, it is not conclusive that SHS is using exactly the same mechanisms as direct smoke in COPD pathogenesis, but should be considered a preventable health risk. Some characteristics and therapeutic alternatives uniquely exist in SHS-related COPD.

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.

In vitro and in vivo characterization of a novel soluble epoxide hydrolase inhibitor

Soluble epoxide hydrolase (sEH, EPHX2) metabolizes eicosanoid epoxides, including epoxyeicosatrienoic acids (EETs) to the corresponding dihydroxyeicosatrienoic acids (DHETs), and leukotoxin (LTX) to leukotoxin diol (LTX diol). EETs, endothelium-derived hyperpolarizing factors, exhibit potentially beneficial properties, including anti-inflammatory effects and vasodilation. A novel, potent, selective inhibitor of recombinant human, rat and mouse sEH, GSK2256294A, exhibited potent cell-based activity, a concentration-dependent inhibition of the conversion of 14,15-EET to 14,15-DHET in human, rat and mouse whole blood in vitro, and a dose-dependent increase in the LTX/LTX diol ratio in rat plasma following oral administration. Mice receiving 10 days of cigarette smoke exposure concomitant with oral administration of GSK2256294A exhibited significant, dose-dependent reductions in pulmonary leukocytes and keratinocyte chemoattractant (KC, CXCL1) levels. Mice receiving oral administration of GSK2256294A following 10 days of cigarette smoke exposure exhibited significant reductions in pulmonary leukocytes compared to vehicle-treated mice. These data indicate that GSK2256294A attenuates cigarette smoke-induced inflammation by both inhibiting its initiation and/or maintenance and promoting its resolution. Collectively, these data indicate that GSK2256294A would be an appropriate agent to evaluate the role of sEH in clinical studies, for example in diseases where cigarette smoke is a risk factor, such as chronic obstructive pulmonary disease (COPD) and cardiovascular disease.

Upregulation of soluble epoxide hydrolase in proximal tubular cells mediated proteinuria-induced renal damage

Epoxyeicosatrienoic acids, hydrolyzed by soluble epoxide hydrolase (sEH), have multiple biological functions, including the regulation of vascular tone, renal tubular transport, and being anti-inflammatory. Inhibitors of sEH have been demonstrated to be antihypertensive and renal protective. To elucidate the role of sEH in glomerulonephritis, we first determined the expression of sEH in human kidney by examining biopsies from 153 patients with a variety of glomerulonephritis, including minimal-change, membranous, and IgA nephropathy. Immunohistochemical staining of frozen kidney biopsy samples revealed sEH preferentially expressed in the renal proximal tubular cells, and its expression increased in all patients with glomerulonephritis. The level of sEH in the cortex was positively correlated with proteinuria and negatively with serum albumin level. To investigate the role of sEH in proteinuria-induced renal damage, we incubated purified urine protein from patients with rat renal proximal tubular epithelial cells in vitro. The level of sEH was elevated, as were monocyte chemoattractant protein 1 and the process of tubular epithelial-to-mesenchymal transition, characterized with increased α-smooth muscle actin (α-SMA) and decreased E-cadherin. These effects were attenuated by administration of a potent sEH inhibitor and mimicked with adenovirus-mediated sEH overexpression. In adriamycin-induced nephropathic mice, sEH inhibitor did not ameliorate proteinuria or level of serum albumin but reduced the long-term elevated serum creatinine level, interstitial inflammation, fibrosis, and α-SMA expression. Thus upregulation of sEH in proximal tubular cells in chronic proteinuric kidney diseases may mediate proteinuria-induced renal damage; sEH inhibition by increasing renal eicosanoid levels could prevent the progression of chronic proteinuric kidney diseases.

Soluble epoxide hydrolase gene deficiency or inhibition attenuates chronic active inflammatory bowel disease in IL-10(-/-) mice

BACKGROUND

Soluble epoxide hydrolase (sEH) metabolizes anti-inflammatory epoxyeicosatrienoic acids (EETs) into their much less active dihydroxy derivatives dihydroxyeicosatrienoic acids. Thus, targeting sEH would be important for inflammation.

AIMS

To determine whether knockout or inhibition of sEH would attenuate the development of inflammatory bowel disease (IBD) in a mouse model of IBD in IL-10(-/-) mice.

METHODS

Either the small molecule sEH inhibitor trans/-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB) or sEH knockout mice were used in combination with IL-10(-/-) mice. t-AUCB was administered to mice in drinking fluid. Extensive histopathologic, immunochemical, and biochemical analyses were performed to evaluate effect of sEH inhibition or deficiency on chronic active inflammation and related mechanism in the bowel.

RESULTS

Compared to IL-10 (-/-) mice, sEH inhibition or sEH deficiency in IL-10(-/-) mice resulted in significantly lower incidence of active ulcer formation and transmural inflammation, along with a significant decrease in myeloperoxidase-labeled neutrophil infiltration in the inflamed bowel. The levels of IFN-γ, TNF-α, and MCP-1, as well VCAM-1 and NF-kB/IKK-α signals were significantly decreased as compared to control animals. Moreover, an eicosanoid profile analysis revealed a significant increase in the ratio of EETs/DHET and EpOME/DiOME, and a slightly down-regulation of inflammatory mediators LTB(4) and 5-HETE.

CONCLUSION

These results indicate that sEH gene deficiency or inhibition reduces inflammatory activities in the IL-10 (-/-) mouse model of IBD, and that sEH inhibitor could be a highly potential in the treatment of IBD.

EH3 (ABHD9): the first member of a new epoxide hydrolase family with high activity for fatty acid epoxides

Epoxide hydrolases are a small superfamily of enzymes important for the detoxification of chemically reactive xenobiotic epoxides and for the processing of endogenous epoxides that act as signaling molecules. Here, we report the identification of two human epoxide hydrolases: EH3 and EH4. They share 45% sequence identity, thus representing a new family of mammalian epoxide hydrolases. Quantitative RT-PCR from mouse tissue indicates strongest EH3 expression in lung, skin, and upper gastrointestinal tract. The recombinant enzyme shows a high turnover number with 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid (EET), as well as 9,10-epoxyoctadec-11-enoic acid (leukotoxin). It is inhibited by a subclass of N,N'-disubstituted urea derivatives, including 12-(3-adamantan-1-yl-ureido)-dodecanoic acid, 1-cyclohexyl-3-dodecylurea, and 1-(1-acetylpiperidin-4-yl)-3-(4-(trifluoromethoxy)phenyl)urea, compounds so far believed to be selective inhibitors of mammalian soluble epoxide hydrolase (sEH). Its sensitivity to this subset of sEH inhibitors may have implications on the pharmacologic profile of these compounds. This is particularly relevant because sEH is a potential drug target, and clinical trials are under way exploring the value of sEH inhibitors in the treatment of hypertension and diabetes type II.

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.

Biologically active ester derivatives as potent inhibitors of the soluble epoxide hydrolase

Substituted ureas with a carboxylic acid ester as a secondary pharmacophore are potent soluble epoxide hydrolase (sEH) inhibitors. Although the ester substituent imparts better physical properties, such compounds are quickly metabolized to the corresponding less potent acids. Toward producing biologically active ester compounds, a series of esters were prepared and evaluated for potency on the human enzyme, stability in human liver microsomes, and physical properties. Modifications around the ester function enhanced in vitro metabolic stability of the ester inhibitors up to 32-fold without a decrease in inhibition potency. Further, several compounds had improved physical properties.

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.

8,9-Epoxyeicosatrienoic acid inhibits antibody production of B lymphocytes in mice

Epoxyeicosatrienoic acids (EETs), synthesized from arachidonic acid by cytochrome P450 epoxygenases, are converted to dihydroxyeicosatrienoic acids by soluble epoxide hydrolase. EETs exert anti-inflammatory effects. However, the effect of EETs on humoral immunity is poorly understood. The present study is to investigate the potential role of EETs on B cell function and mechanisms. We examined the role of EETs on antibody production of splenic B cells from C57BL/6 and apolipoprotein E-deficient (ApoE−/−) mice by means of ELISA. Of the 4 EET regioisomers, 8,9-EET decreased basal and activation-induced B cell antibody secretion. As well, 8,9-EET significantly inhibited B-cell proliferation and survival, plasma cell differentiation and class-switch recombination. Western blot analysis revealed that lipopolysaccharide-induced nuclear translocation of NF-κB could be attenuated by 8,9-EET. Furthermore, germinal center formation was impaired by 8,9-EET in mice in vivo. 8,9-EET may inhibit B-cell function in vitro and in vivo, which suggests a new therapeutic strategy for diseases with excess B cell activation.

Soluble epoxide hydrolase regulates hematopoietic progenitor cell function via generation of fatty acid diols

Fatty acid epoxides are important lipid signaling molecules involved in the regulation of vascular tone and homeostasis. Tissue and plasma levels of these mediators are determined by the activity of cytochrome P450 epoxygenases and the soluble epoxide hydrolase (sEH), and targeting the latter is an effective way of manipulating epoxide levels in vivo. We investigated the role of the sEH in regulating the mobilization and proliferation of progenitor cells with vasculogenic/reparative potential. Our studies revealed that sEH down-regulation/inhibition impaired the development of the caudal vein plexus in zebrafish, and decreased the numbers of lmo2/cmyb-positive progenitor cells therein. In mice sEH inactivation attenuated progenitor cell proliferation (spleen colony formation), but the sEH products 12,13-dihydroxyoctadecenoic acid (12,13-DiHOME) and 11,12- dihydroxyeicosatrienoic acid stimulated canonical Wnt signaling and rescued the effects of sEH inhibition. In murine bone marrow, the epoxide/diol content increased during G-CSF-induced progenitor cell expansion and mobilization, and both mobilization and spleen colony formation were reduced in sEH(-/-) mice. Similarly, sEH(-/-) mice showed impaired functional recovery following hindlimb ischemia, which was rescued following either the restoration of bone marrow sEH activity or treatment with 12,13-DiHOME. Thus, sEH activity is required for optimal progenitor cell proliferation, whereas long-term sEH inhibition is detrimental to progenitor cell proliferation, mobilization, and vascular repair.

Attenuation of cisplatin-induced renal injury by inhibition of soluble epoxide hydrolase involves nuclear factor κB signaling

Acute kidney injury is associated with a significant inflammatory response that has been the target of renoprotection strategies. Epoxyeicosatrienoic acids (EETs) are anti-inflammatory cytochrome P450-derived eicosanoids that are abundantly produced in the kidney and metabolized by soluble epoxide hydrolase (sEH; Ephx2) to less active dihydroxyeicosatrienoic acids. Genetic disruption of Ephx2 and chemical inhibition of sEH were used to test whether the anti-inflammatory effects of EETs, and other lipid epoxide substrates of sEH, afford protection against cisplatin-induced nephrotoxicity. EET hydrolysis was significantly reduced in Ephx2(-/-) mice and was associated with an attenuation of cisplatin-induced increases in serum urea nitrogen and creatinine levels. Histological evidence of renal tubular damage and neutrophil infiltration was also reduced in the Ephx2(-/-) mice. Likewise, cisplatin had no effect on renal function, neutrophil infiltration, or tubular structure and integrity in mice treated with the potent sEH inhibitor 1-adamantan-1-yl-3-(1-methylsulfonyl-piperidin-4-yl-urea) (AR9273). Consistent with the ability of EETs to interfere with nuclear factor-κB (NF-κB) signaling, the observed renoprotection was associated with attenuation of renal NF-κB activity and corresponding decreases in the expression of tumor necrosis factor (TNF) α, TNF receptor (TNFR) 1, TNFR2, and intercellular adhesive molecule-1 before the detection of tubular injury. These data suggest that EETs or other fatty acid epoxides can attenuate cisplatin-induced kidney injury and sEH inhibition is a novel renoprotective strategy.

The influence of cigarette smoke on the selected bronchoalveolar cells in experiment

The occurence of lung diseases (obstructive, malignant) resulting from smoking has an increasing tendency. The lung is the primary organ at risk from the effects of inhaled cigarette smoke and smoking has been implicated as a contributing factor to the causation of various respiratory diseases. The aim of presented work was to find out the subchronic effect of the 6-month exposure to cigarette smoke on the selected inflammatory and cytotoxic parameters of bronchoalveolar lavage in W rats and thus to contribute to understanding of the mechanism of action of tobacco smoke and/or path mechanism of lung injury developed after cigarette smoking. In special chamber, the animals smoked 8 standard research 1R1 type of cigarettes per day, except Saturdays and Sundays, during 6 months. The daily concentration of total particulate matter (TPM)/m3 air for two hours per exposure requiring to burn eight cigarettes was 85 mg. Animals were sacrificed after the 6-month exposure and bronchoalveolar lavage (BAL) was performed and selected inflammatory and cytotoxic BAL parameters were examined and compared with the control group. Following BAL parameters were investigated: the total cell and alveolar macrophages (AM) count in BAL, the differential cell count (% of AM, % of polymorphonuclears--PMN, % of lymphocytes--Ly), proportion of immature AM, proportion of bi-nucleated cells--BNC, viability, the phagocytic activity of AM, cytokines TNF-alpha (tumor necrosis factor alpha) and IL-1beta (interleukin-1beta).

CONCLUSION

A) The 6-month smoking of eight cigarettes daily significantly changed prevailing number of examined BAL parameters; B) The presence of inflammatory and cytotoxic responses in lung tissue can probably signalize beginning or developing of disease process.

Use of a soluble epoxide hydrolase inhibitor in smoke-induced chronic obstructive pulmonary disease

Tobacco smoke-induced chronic obstructive pulmonary disease (COPD) is a prolonged inflammatory condition of the lungs characterized by progressive and largely irreversible airflow limitation attributable to a number of pathologic mechanisms, including bronchitis, bronchiolitis, emphysema, mucus plugging, pulmonary hypertension, and small-airway obstruction. Soluble epoxide hydrolase inhibitors (sEHIs) demonstrated anti-inflammatory properties in a rat model after acute exposure to tobacco smoke. We compared the efficacy of sEHI t-TUCB (trans-4-{4-[3-(4-trifluoromethoxy-phenyl)-ureido]-cyclohexyloxy}-benzoic acid) and the phosphodiesterase-4 (PDE4) inhibitor Rolipram (Biomol International, Enzo Life Sciences, Farmingdale, NY) to reduce lung injury and inflammation after subacute exposure to tobacco smoke over a period of 4 weeks. Pulmonary physiology, bronchoalveolar lavage, cytokine production, and histopathology were analyzed to determine the efficacy of sEHI and Rolipram to ameliorate tobacco smoke-induced inflammation and injury in the spontaneously hypertensive rat. Both t-TUCB and Rolipram inhibited neutrophil elevation in bronchoalveolar lavage. sEHI t-TUCB suppressed IFN-γ, while improving lung function by reducing tobacco smoke-induced total respiratory resistance and tissue damping (small-airway and peripheral tissue resistance). Increases in tobacco smoke-induced alveolar airspace size were attenuated by t-TUCB. Rolipram inhibited the production of airway mucus. Both t-TUCB and Rolipram inhibited vascular remodeling-related growth factor. These findings suggest that sEHI t-TUCB has therapeutic potential for treating COPD by improving lung function and attenuating the lung inflammation and emphysematous changes caused by tobacco smoke. To the best of our knowledge, this is the first report to demonstrate that sEHI exerts significant protective effects after repeated, subacute tobacco smoke-induced lung injury in a rat model of COPD.

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.

2,3,7,8-Tetrachlorodibenzo-p-dioxin treatment alters eicosanoid levels in several organs of the mouse in an aryl hydrocarbon receptor-dependent fashion

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) adversely affects many mammalian organs and tissues. These effects are mediated by the aryl hydrocarbon receptor (AHR). CYP1A1, CYP1A2 and CYP1B1 are upregulated by the liganded AHR. These (and other) cytochromes P450 can metabolize arachidonic acid into a variety of bioactive eicosanoids. Towards investigating a potential role of eicosanoids in TCDD toxicity, arachidonic acid, two other unsaturated long-chain fatty acids, and up to twenty-five eicosanoids were measured in five organs/tissues of male and female wild-type and Ahr null mice treated or untreated with TCDD. TCDD generally increased the levels of the four dihydroxyeicosatrienoic acids (DHETs) and (where measured) 5,6-epoxyeicosatrienoic acid and 18-, 19- and 20-hydroxyeicosatrienoic acids (HETEs) in the serum, liver, spleen and lungs, but not the heart, of both sexes, and increased the levels in the serum, liver and spleen of several metabolites that are usually considered products of lipoxygenase activity, but which may also be generated by cytochromes P450. TCDD also increased the levels of the esterified forms of these eicosanoids in the liver in parallel with the corresponding free forms. The levels of prostanoids were generally not affected by TCDD. The above changes did not occur in Ahr null mice, and are therefore mediated by the AHR. TCDD increased the mRNA levels of Cyp1a1, Cyp1a2, Cyp1b1 and the Pla2g12a form of phospholipase A(2) to varying degrees in the different organs, and these increases correlated with some but not all the changes in eicosanoids levels in the organs, suggesting that other enzymes may also be involved.

The anti-inflammatory effects of soluble epoxide hydrolase inhibitors are independent of leukocyte recruitment

Excess leukocyte recruitment to the lung plays a central role in the development or exacerbation of several lung inflammatory diseases including chronic obstructive pulmonary disease. Epoxyeicosatrienoic acids (EETs) are cytochrome P-450 metabolites of arachidonic acid reported to have multiple biological functions, including blocking of leukocyte recruitment to inflamed endothelium in cell culture through reduction of adhesion molecule expression. Inhibition of the EET regulatory enzyme, soluble epoxide hydrolase (sEH) also has been reported to have anti-inflammatory effects in vivo including reduced leukocyte recruitment to the lung. We tested the hypothesis that the in vivo anti-inflammatory effects of sEH inhibitors act through the same mechanisms as the in vitro anti-inflammatory effects of EETs in a rat model of acute inflammation following exposure to tobacco smoke. Contrary to previously published data, we found that sEH inhibition did not reduce tobacco smoke-induced leukocyte recruitment to the lung. Furthermore, sEH inhibition did not reduce tobacco smoke-induced adhesion molecule expression in the lung vasculature. Similarly, concentrations of EETs greater than or equal to their reported effective dose did not reduce TNFα induced expression of the adhesion molecules. These results suggest that the anti-inflammatory effects of sEH inhibitors are independent of leukocyte recruitment and EETs do not reduce the adhesion molecules responsible for leukocyte recruitment in vitro. This demonstrates that the widely held belief that sEH inhibition prevents leukocyte recruitment via EET prevention of adhesion molecule expression is not consistently reproducible.

Investigation of utilization of nanosuspension formulation to enhance exposure of 1,3-dicyclohexylurea in rats: Preparation for PK/PD study via subcutaneous route of nanosuspension drug delivery

1,3-Dicyclohexylurea (DCU), a potent soluble epoxide hydrolase (sEH) inhibitor has been reported to lower systemic blood pressure in spontaneously hypertensive rats. One limitation of continual administration of DCU for in vivo studies is the compound's poor oral bioavailability. This phenomenon is mainly attributed to its poor dissolution rate and low aqueous solubility. Previously, wet-milled DCU nanosuspension has been reported to enhance the bioavailability of DCU. However, the prosperities and limitations of wet-milled nanosuspension have not been fully evaluated. Furthermore, the oral pharmacokinetics of DCU in rodent are such that the use of DCU to understand PK/PD relationships of sEH inhibitors in preclinical efficacy model is less than ideal. In this study, the limitation of orally delivered DCU nanosuspension was assessed by a surface area sensitive absorption model and pharmacokinetic modeling. It was found that dosing DCU nanosuspension did not provide the desired plasma profile needed for PK/PD investigation. Based on the model and in vivo data, a subcutaneous route of delivery of nanosuspension of DCU was evaluated and demonstrated to be appropriate for future PK/PD studies.

Epoxygenated fatty acids and soluble epoxide hydrolase inhibition: novel mediators of pain reduction

The soluble epoxide hydrolase (sEH) enzyme was discovered while investigating the metabolism of xenobiotic compounds in the Casida laboratory. However, an endogenous role of sEH is to regulate the levels of a group of potent bioactive lipids, epoxygenated fatty acids (EFAs), that have pleiotropic biological activities. The EFAs, in particular the arachidonic acid derived epoxy eicosatrienoic acids (EETs), are established autocrine and paracrine messengers. The most recently discovered outcome of inhibition of sEH and increased EFAs is their effects on the sensory system and in particular their ability to reduce pain. The inhibitors of sEH block both inflammatory and neuropathic pain. Elevation of EFAs, in both the central and peripheral nervous systems, blocks pain. Several laboratories have now published a number of potential mechanisms of action for the pain-reducing effects of EFAs. This paper provides a brief history of the discovery of the sEH enzyme and argues that inhibitors of sEH through several independent mechanisms display pain-reducing effects.

Structure-activity relationships of cycloalkylamide derivatives as inhibitors of the soluble epoxide hydrolase

Structure-activity relationships of cycloalkylamide compounds as inhibitors of human sEH were investigated. When the left side of amide function was modified by a variety of cycloalkanes, at least a C6 like cyclohexane was necessary to yield reasonable inhibition potency on the target enzyme. In compounds with a smaller cycloalkane or with a polar group on the left side of amide function, no inhibition was observed. On the other hand, increased hydrophobicity dramatically improved inhibition potency. Especially, a tetrahydronaphthalene (20) effectively increased the potency. When a series of alkyl or aryl derivatives of cycloalkylamide were investigated to continuously optimize the right side of the amide pharmacophore, a benzyl moiety functionalized with a polar group produced highly potent inhibition. A nonsubstituted benzyl, alkyl, aryl, or biaryl structure present on the right side of the cycloalkylamide function induced a big decrease in inhibition potency. Also, the resulting potent cycloalkylamide (32) showed reasonable physical properties.

1-(1-acetyl-piperidin-4-yl)-3-adamantan-1-yl-urea (AR9281) as a potent, selective, and orally available soluble epoxide hydrolase inhibitor with efficacy in rodent models of hypertension and dysglycemia

1-(1-Acetyl-piperidin-4-yl)-3-adamantan-1-yl-urea 14a (AR9281), a potent and selective soluble epoxide hydrolase inhibitor, was recently tested in a phase 2a clinical setting for its effectiveness in reducing blood pressure and improving insulin resistance in pre-diabetic patients. In a mouse model of diet induced obesity, AR9281 attenuated the enhanced glucose excursion following an intraperitoneal glucose tolerance test. AR9281 also attenuated the increase in blood pressure in angiotensin-II-induced hypertension in rats. These effects were dose-dependent and well correlated with inhibition of the sEH activity in whole blood, consistent with a role of sEH in the observed pharmacology in rodents.

Mammalian soluble epoxide hydrolase is identical to liver hepoxilin hydrolase

Hepoxilins are lipid signaling molecules derived from arachidonic acid through the 12-lipoxygenase pathway. These trans-epoxy hydroxy eicosanoids play a role in a variety of physiological processes, including inflammation, neurotransmission, and formation of skin barrier function. Mammalian hepoxilin hydrolase, partly purified from rat liver, has earlier been reported to degrade hepoxilins to trioxilins. Here, we report that hepoxilin hydrolysis in liver is mainly catalyzed by soluble epoxide hydrolase (sEH): i) purified mammalian sEH hydrolyses hepoxilin A₃ and B₃ with a V(max) of 0.4-2.5 μmol/mg/min; ii) the highly selective sEH inhibitors N-adamantyl-N'-cyclohexyl urea and 12-(3-adamantan-1-yl-ureido) dodecanoic acid greatly reduced hepoxilin hydrolysis in mouse liver preparations; iii) hepoxilin hydrolase activity was abolished in liver preparations from sEH(-/-) mice; and iv) liver homogenates of sEH(-/-) mice show elevated basal levels of hepoxilins but lowered levels of trioxilins compared with wild-type animals. We conclude that sEH is identical to previously reported hepoxilin hydrolase. This is of particular physiological relevance because sEH is emerging as a novel drug target due to its major role in the hydrolysis of important lipid signaling molecules such as epoxyeicosatrienoic acids. sEH inhibitors might have undesired side effects on hepoxilin signaling.

Endothelial CYP epoxygenase overexpression and soluble epoxide hydrolase disruption attenuate acute vascular inflammatory responses in mice

Cytochrome P-450 (CYP)-derived epoxyeicosatrienoic acids (EETs) possess potent anti-inflammatory effects in vitro. However, the effect of increased CYP-mediated EET biosynthesis and decreased soluble epoxide hydrolase (sEH, Ephx2)-mediated EET hydrolysis on vascular inflammation in vivo has not been rigorously investigated. Consequently, we characterized acute vascular inflammatory responses to endotoxin in transgenic mice with endothelial expression of the human CYP2J2 and CYP2C8 epoxygenases and mice with targeted disruption of Ephx2. Compared to wild-type controls, CYP2J2 transgenic, CYP2C8 transgenic, and Ephx2(-/-) mice each exhibited a significant attenuation of endotoxin-induced activation of nuclear factor (NF)-κB signaling, cellular adhesion molecule, chemokine and cytokine expression, and neutrophil infiltration in lung in vivo. Furthermore, attenuation of endotoxin-induced NF-κB activation and cellular adhesion molecule and chemokine expression was observed in primary pulmonary endothelial cells isolated from CYP2J2 and CYP2C8 transgenic mice. This attenuation was inhibited by a putative EET receptor antagonist and CYP epoxygenase inhibitor, directly implicating CYP epoxygenase-derived EETs with the observed anti-inflammatory phenotype. Collectively, these data demonstrate that potentiation of the CYP epoxygenase pathway by either increased endothelial EET biosynthesis or globally decreased EET hydrolysis attenuates NF-κB-dependent vascular inflammatory responses in vivo and may serve as a viable anti-inflammatory therapeutic strategy.

Red blood cells (RBCs), epoxyeicosatrienoic acids (EETs) and adenosine triphosphate (ATP)

In addition to serving as carriers of O(2), red blood cells (RBCs) regulate vascular resistance and the distribution of microvascular perfusion by liberating adenosine triphosphate (ATP) and epoxyeicosatrienoic acids (EETs) upon exposure to a low O(2) environment. Therefore, RBCs act as sensors that respond to low pO(2) by releasing millimolar amounts of ATP, a signaling molecule, and lipid mediators (EETs). The release of EETs occurs by a mechanism that is activated by ATP stimulation of P2X(7) receptors coupled to ATP transporters, which should greatly amplify the circulatory response to ATP. RBCs are reservoirs of EETs and the primary sources of plasma EETs, which are esterified to the phospholipids of lipoproteins. Levels of free EETs in plasma are low, about 3% of circulating EETs. RBC EETs are produced by direct oxidation of arachidonic acid (AA) esterified to glycerophospholipids and the monooxygenase-like activity of hemoglobin. On release, EETs affect vascular tone, produce profibrinolysis and dampen inflammation. A soluble epoxide hydrolase (sEH) regulates the concentrations of RBC and vascular EETs by metabolizing both cis- and trans-EETs to form dihydroxyeicosatrienoic acids (DHETs). The function and pathophysiological roles of trans-EETs and erythro-DHETs has yet to be integrated into a physiological and pathophysiological context.

Chronic treatment with epoxyeicosatrienoic acids modulates insulin signaling and prevents insulin resistance in hepatocytes

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites produced by cytochrome P450 epoxygenases which are highly expressed in hepatocytes. The functions of EETs in hepatocytes are not well understood. In this study, we investigated the effects of 14,15-EETs treatment on the insulin signal transduction pathway in hepatocytes. We report that chronic treatment, not acute treatment, with 30 μM 14,15-EETs prevents palmitate induced insulin resistance and potentiates insulin action in cultured HepG2 hepatocytes. 14,15-EETs increase Akt phosphorylation at S473, activating Akt, in an insulin dependent manner in HepG2 cells. Under insulin resistant conditions induced by palmitate, 14,15-EETs restore the insulin response by increasing S473-phosphorylated Akt. 8,9-EETs and 11,12-EETs demonstrated similar effects to 14,15-EETs. Furthermore, 14,15-EETs potentiate insulin-suppression of gluconeogenesis in cultured H4IIE hepatocytes. To elucidate the mechanism of EETs function, we analyzed the insulin signaling factors upstream of Akt. Inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 attenuated the 14,15-EETs-induced activating phosphorylation of Akt. 14,15-EETs reduced palmitate-stimulated phosphorylation of IRS-1 on S312 and phosphorylation of c-Jun N-terminal kinase (JNK) at threonine 183 and tyrosine 185 residues. The regulation of insulin sensitivity in cultured hepatocytes by chronic 14,15-EETs treatment appears to involve the JNK-IRS-PI3K pathway. The requirement of chronic treatment with EETs suggests that the effects of EETs on insulin response may be indirect.

Role of cytochrome P450 enzymes in the bioactivation of polyunsaturated fatty acids

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA), such as epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid, serve as second messengers of various hormones and growth factors and play pivotal roles in the regulation of vascular, renal and cardiac function. As discussed in the present review, virtually all of the major AA metabolizing CYP isoforms accept a variety of other polyunsaturated fatty acids (PUFA), including linoleic, eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), as efficient alternative substrates. The metabolites of these alternative PUFAs also elicit profound biological effects. The CYP enzymes respond to alterations in the chain-length and double bond structure of their substrates with remarkable changes in the regio- and stereoselectivity of product formation. The omega-3 double bond that distinguishes EPA and DHA from their omega-6 counterparts provides a preferred epoxidation site for CYP1A, CYP2C, CYP2J and CYP2E subfamily members. CYP4A enzymes that predominantly function as AA ω-hydroxylases show largely increased (ω-1)-hydroxylase activities towards EPA and DHA. Taken together, these findings indicate that CYP-dependent signaling pathways are highly susceptible to changes in the relative bioavailability of the different PUFAs and may provide novel insight into the complex mechanisms that link essential dietary fatty acids to the development of cardiovascular disease.