Distribution of soluble and microsomal epoxide hydrolase in the mouse brain and its contribution to cerebral epoxyeicosatrienoic acid metabolism

Paraoxonase 1 in endothelial cells impairs vasodilation induced by arachidonic acid lactone metabolite

INTRODUCTION

Paraoxonase 1 (PON1) is a high density lipoprotein (HDL)-associated lactonase, which is known for its antiatherogenic properties. Previous studies in PON1 knockout (PON1KO) mice revealed that PON1KO mice have low blood pressure, which is inversely correlated with the renal levels of the cytochrome P450 -derived arachidonic acid metabolite 5,6-epoxyeicosatrienoic acid (5,6-EET). Our previous studies revealed that 5,6-EET is unstable, transforming to the δ-lactone isomer 5,6-δ-DHTL, an endothelium-derived hyperpolarizing factor (EDHF) that mediates vasodilation, and it is a potential substrate for PON1.

AIM

To elucidate the role of PON1 in the modulation of vascular resistance via the regulation of the lactone-containing metabolite 5,6-δ-DHTL.

RESULTS

In mouse resistance arteries, PON1 was found to be present and active in the endothelial layer. Vascular reactivity experiments revealed that 5,6-δ-DHTL dose-dependently dilates PON1KO mouse mesenteric arteries significantly more than wild type (w.t.) resistance arteries. Pre-incubation with HDL or rePON1 reduced 5,6-δ-DHTL-dependent vasodilation. FACS analyses and confocal microscopy experiments revealed that fluorescence-tagged rePON1 penetrates into human endothelial cells' (ECs') in both dose- and time- dependent manner, accumulate in the perinuclear compartment, and retains its lactonase activity in the cells. The presence of rePON1, but not the presence of PON1 loss-of-lactonase-activity mutant, reduced the Ca²⁺ influx in the ECs mediated by 5,6-δ-DHTL.

CONCLUSION

PON1 lactonase activity in the endothelium affects vascular dilation by regulating Ca²⁺ influx mediated by the lactone-containing EDHF 5,6-δ-DHTL.

An optimized radiosynthesis of [18 F]FNDP, a positron emission tomography radiotracer for imaging soluble epoxide hydrolase (sEH)

In this concise practitioner protocol, the radiochemical synthesis of [¹⁸ F]FNDP suitable for human positron emission tomography studies is described and the results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice requirements.

Soluble epoxide hydrolase inhibition decreases reperfusion injury after focal cerebral ischemia

Epoxyeicosatrienoic acids (EETs) are produced by cytochrome P450 epoxygenases from arachidonic acid, and their rapid metabolism is mainly through soluble epoxide hydrolase (sEH). EETs exert vasodilatory, anti-inflammatory, anti-apoptotic, and pro-angiogenic effects. Administration of sEH inhibitors before or at the onset of stroke is protective, but the effects of post-treatment at reperfusion, when inflammation is augmented, has not been as well studied. We tested the hypothesis that 1-Trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea (TPPU), a potent and highly selective sEH inhibitor, suppresses inflammation and protects the brain when administered at reperfusion. Vehicle or 1 mg/kg TPPU was administered at reperfusion after 90 minutes of focal ischemia and again 24 hours later. Protein expression and activity of sEH increased after reperfusion and activity was decreased by TPPU administration. TPPU decreased infarct volume by 50%, reduced neurologic deficits and improved performance on sensorimotor tasks. Furthermore, TPPU significantly lowered the mRNA expression of interleukin-1beta by 3.5-fold and tumor necrosis factor-alpha by 2.2-fold, increased transforming growth factor-beta mRNA by 1.8-fold, and augmented immunostaining of vascular endothelial growth factor in peri-infarct cortex. Thus, inhibition of sEH at reperfusion significantly reduces infarction and improves sensorimotor function, possibly by suppressing early proinflammatory cytokines and promoting reparative cytokines and growth factors.

Regulation of Cerebral Blood Flow: Response to Cytochrome P450 Lipid Metabolites

There have been numerous reviews related to the cerebral circulation. Most of these reviews are similar in many ways. In the present review, we thought it important to provide an overview of function with specific attention to details of cerebral arterial control related to brain homeostasis, maintenance of neuronal energy demands, and a unique perspective related to the role of astrocytes. A coming review in this series will discuss cerebral vascular development and unique properties of the neonatal circulation and developing brain, thus, many aspects of development are missing here. Similarly, a review of the response of the brain and cerebral circulation to heat stress has recently appeared in this series (8). By trying to make this review unique, some obvious topics were not discussed in lieu of others, which are from recent and provocative research such as endothelium-derived hyperpolarizing factor, circadian regulation of proteins effecting cerebral blood flow, and unique properties of the neurovascular unit. © 2018 American Physiological Society. Compr Physiol 8:801-821, 2018.

Blockade of soluble epoxide hydrolase attenuates post-ischemic neuronal hyperexcitation and confers resilience against stroke with TrkB activation

Inhibition and deletion of soluble epoxide hydrolase (sEH) has been suggested to ameliorate infarction in experimental ischemic stroke possibly via vasoactive epoxyeicosatrienoic acids. However, it is unknown whether the neuroprotective mechanisms involve alteration of post-ischemic neuronal transmission and neurotrophic signaling. We used a permanent middle cerebral artery occlusion (MCAO) model in adult wild-type mice with the sEH inhibitor 12-(3-adamantan-1-yl-ureido)dodecanoic acid (AUDA) post-treatment and in sEH knockout (sEH KO) mice. We found that sensorimotor recovery was significantly enhanced after MCAO in both AUDA-treated and sEH KO mice, with decreased sEH activity and brain infarction. Decreased post-ischemic long-term potentiation (iLTP) was observed in an ex vivo hippocampal oxygen-glucose deprivation model. Tropomyosin receptor kinase B (TrkB) activation, rather than glutamate receptor alteration, was consistently found after the different manipulations. Immunohistochemistry further revealed peri-infarct neuronal TrkB activation and microvasculature augmentation in AUDA-treated and sEH KO mice, suggesting parallel neurovascular enhancement. Mechanistically, pretreatment with a selective TrkB antagonist ANA12 countered the effect of iLTP attenuation induced by sEH deletion ex vivo and abolished the infarct reduction in vivo. Together, the neuroprotective effects of sEH inhibition and gene deletion can both be mediated partially via enhancement of TrkB signaling which attenuated post-ischemic neuroexcitation and neurological deficits.

Epoxide hydrolase 1 (EPHX1) hydrolyzes epoxyeicosanoids and impairs cardiac recovery after ischemia

Stimuli such as inflammation or hypoxia induce cytochrome P450 epoxygenase-mediated production of arachidonic acid-derived epoxyeicosatrienoic acids (EETs). EETs have cardioprotective, vasodilatory, angiogenic, anti-inflammatory, and analgesic effects, which are diminished by EET hydrolysis yielding biologically less active dihydroxyeicosatrienoic acids (DHETs). Previous in vitro assays have suggested that epoxide hydrolase 2 (EPHX2) is responsible for nearly all EET hydrolysis. EPHX1, which exhibits slow EET hydrolysis in vitro, is thought to contribute only marginally to EET hydrolysis. Using Ephx1^-/-, Ephx2^-/-, and Ephx1^-/-Ephx2^-/- mice, we show here that EPHX1 significantly contributes to EET hydrolysis in vivo Disruption of Ephx1 and/or Ephx2 genes did not induce compensatory changes in expression of other Ephx genes or CYP2 family epoxygenases. Plasma levels of 8,9-, 11,12-, and 14,15-DHET were reduced by 38, 44, and 67% in Ephx2^-/- mice compared with wildtype (WT) mice, respectively; however, plasma from Ephx1^-/-Ephx2^-/- mice exhibited significantly greater reduction (100, 99, and 96%) of those respective DHETs. Kinetic assays and FRET experiments indicated that EPHX1 is a slow EET scavenger, but hydrolyzes EETs in a coupled reaction with cytochrome P450 to limit basal EET levels. Moreover, we also found that EPHX1 activities are biologically relevant, as Ephx1^-/-Ephx2^-/- hearts had significantly better postischemic functional recovery (71%) than both WT (31%) and Ephx2^-/- (51%) hearts. These findings indicate that Ephx1^-/-Ephx2^-/- mice are a valuable model for assessing EET-mediated effects, uncover a new paradigm for EET metabolism, and suggest that dual EPHX1 and EPHX2 inhibition may represent a therapeutic approach to manage human pathologies such as myocardial infarction.

Soluble epoxide hydrolase as a therapeutic target for pain, inflammatory and neurodegenerative diseases

Eicosanoids are biologically active lipid signaling molecules derived from polyunsaturated fatty acids. Many of the actions of eicosanoid metabolites formed by cyclooxygenase and lipoxygenase enzymes have been characterized, however, the epoxy-fatty acids (EpFAs) formed by cytochrome P450 enzymes are newly described by comparison. The EpFA metabolites modulate a diverse set of physiologic functions that include inflammation and nociception among others. Regulation of EpFAs occurs primarily via release, biosynthesis and enzymatic transformation by the soluble epoxide hydrolase (sEH). Targeting sEH with small molecule inhibitors has enabled observation of the biological activity of the EpFAs in vivo in animal models, greatly contributing to the overall understanding of their role in the inflammatory response. Their role in modulating inflammation has been demonstrated in disease models including cardiovascular pathology and inflammatory pain, but extends to neuroinflammation and neuroinflammatory disease. Moreover, while EpFAs demonstrate activity against inflammatory pain, interestingly, this action extends to blocking chronic neuropathic pain as well. This review outlines the role of modulating sEH and the biological action of EpFAs in models of pain and inflammatory diseases.

Cytochrome P450 eicosanoids in cerebrovascular function and disease

Cytochrome P450 eicosanoids play important roles in brain function and disease through their complementary actions on cell-cell communications within the neurovascular unit (NVU) and mechanisms of brain injury. Epoxy- and hydroxyeicosanoids, respectively formed by cytochrome P450 epoxygenases and ω-hydroxylases, play opposing roles in cerebrovascular function and in pathological processes underlying neural injury, including ischemia, neuroinflammation and oxidative injury. P450 eicosanoids also contribute to cerebrovascular disease risk factors, including hypertension and diabetes. We summarize studies investigating the roles P450 eicosanoids in cerebrovascular physiology and disease to highlight the existing balance between these important lipid signaling molecules, as well as their roles in maintaining neurovascular homeostasis and in acute and chronic neurovascular and neurodegenerative disorders.

Evidence for a complex formation between CYP2J5 and mEH in living cells by FRET analysis of membrane protein interaction in the endoplasmic reticulum (FAMPIR)

The potential complex formation between microsomal epoxide hydrolase (mEH) and cytochrome P450-dependent monooxygenase (CYP) has been a subject of research for many decades. Such an association would enable efficient substrate channeling between CYP and mEH and as such represent an attractive strategy to prevent deleterious accumulation of harmful metabolic by-products such as CYP-generated epoxide intermediates. However, such complex formation is experimentally difficult to prove, because CYP and mEH are membrane-bound proteins that are prone to unspecific aggregation after solubilization. Here, we report the development of a FRET-based procedure to analyze the mEH–CYP interaction in living cells by fluorescence-activated cell sorting. With this non-invasive procedure, we demonstrate that CYP2J5 and mEH associate in the endoplasmic reticulum of recombinant HEK293 cells to the same extent as do CYP2J5 and its indispensible redox partner cytochrome P450 reductase. This presents final proof for a very close proximity of CYP and mEH in the endoplasmic reticulum, compatible with and indicative of their physical interaction. In addition, we provide with FAMPIR a robust and easy-to-implement general method for analyzing the interaction of ER membrane-resident proteins that share a type I topology.

Beyond detoxification: a role for mouse mEH in the hepatic metabolism of endogenous lipids

Microsomal and soluble epoxide hydrolase (mEH and sEH) fulfill apparently distinct roles: Whereas mEH detoxifies xenobiotics, sEH hydrolyzes fatty acid (FA) signaling molecules and is thus implicated in a variety of physiological functions. These epoxy FAs comprise epoxyeicosatrienoic acids (EETs) and epoxy-octadecenoic acids (EpOMEs), which are formed by CYP epoxygenases from arachidonic acid (AA) and linoleic acid, respectively, and then are hydrolyzed to their respective diols, the so-called DHETs and DiHOMEs. Although EETs and EpOMEs are also substrates for mEH, its role in lipid signaling is considered minor due to lower abundance and activity relative to sEH. Surprisingly, we found that in plasma from mEH KO mice, hydrolysis rates for 8,9-EET and 9,10-EpOME were reduced by 50% compared to WT plasma. This strongly suggests that mEH contributes substantially to the turnover of these FA epoxides—despite kinetic parameters being in favor of sEH. Given the crucial role of liver in controlling plasma diol levels, we next studied the capacity of sEH and mEH KO liver microsomes to synthesize DHETs with varying concentrations of AA (1–30 μM) and NADPH. mEH-generated DHET levels were similar to the ones generated by sEH, when AA concentrations were low (1 μM) or epoxygenase activity was curbed by modulating NADPH. With increasing AA concentrations sEH became more dominant and with 30 μM AA produced twice the level of DHETs compared to mEH. Immunohistochemistry of C57BL/6 liver slices further revealed that mEH expression was more widespread than sEH expression. mEH immunoreactivity was detected in hepatocytes, Kupffer cells, endothelial cells, and bile duct epithelial cells, while sEH immunoreactivity was confined to hepatocytes and bile duct epithelial cells. Finally, transcriptome analysis of WT, mEH KO, and sEH KO liver was carried out to discern transcriptional changes associated with the loss of EH genes along the CYP-epoxygenase–EH axis. We found several prominent dysregulations occurring in a parallel manner in both KO livers: (a) gene expression of Ephx1 (encoding for mEH protein) was increased 1.35-fold in sEH KO, while expression of Ephx2 (encoding for sEH protein) was increased 1.4-fold in mEH KO liver; (b) Cyp2c genes, encoding for the predominant epoxygenases in mouse liver, were mostly dysregulated in the same manner in both sEH and mEH KO mice, showing that loss of either EH has a similar impact. Taken together, mEH appears to play a leading role in the hydrolysis of 8,9-EET and 9,10-EpOME and also contributes to the hydrolysis of other FA epoxides. It probably profits from its high affinity for FA epoxides under non-saturating conditions and its close physical proximity to CYP epoxygenases, and compensates its lower abundance by a more widespread expression, being the only EH present in several sEH-lacking cell types.

Modulation of mitochondrial dysfunction and endoplasmic reticulum stress are key mechanisms for the wide-ranging actions of epoxy fatty acids and soluble epoxide hydrolase inhibitors

The arachidonic acid cascade is arguably the most widely known biologic regulatory pathway. Decades after the seminal discoveries involving its cyclooxygenase and lipoxygenase branches, studies of this cascade remain an active area of research. The third and less widely known branch, the cytochrome P450 pathway leads to highly active oxygenated lipid mediators, epoxy fatty acids (EpFAs) and hydroxyeicosatetraenoic acids (HETEs), which are of similar potency to prostanoids and leukotrienes. Unlike the COX and LOX branches, no pharmaceuticals currently are marketed targeting the P450 branch. However, data support therapeutic benefits from modulating these regulatory lipid mediators. This is being approached by stabilizing or mimicking the EpFAs or even by altering the diet. These approaches lead to predominantly beneficial effects on a wide range of apparently unrelated states resulting in an enigma of how this small group of natural chemical mediators can have such diverse effects. EpFAs are degraded by soluble epoxide hydrolase (sEH) and stabilized by inhibiting this enzyme. In this review, we focus on interconnected aspects of reported mechanisms of action of EpFAs and inhibitors of soluble epoxide hydrolase (sEHI). The sEHI and EpFAs are commonly reported to maintain homeostasis under pathological conditions while remaining neutral under normal physiological conditions. Here we provide a conceptual framework for the unique and broad range of biological activities ascribed to epoxy fatty acids. We argue that their mechanism of action pivots on their ability to prevent mitochondrial dysfunction, to reduce subsequent ROS formation and to block resulting cellular signaling cascades, primarily the endoplasmic reticulum stress. By stabilizing the mitochondrial - ROS - ER stress axis, the range of activity of EpFAs and sEHI display an overlap with the disease conditions including diabetes, fibrosis, chronic pain, cardiovascular and neurodegenerative diseases, for which the above outlined mechanisms play key roles.

Cyclooxygenase-derived proangiogenic metabolites of epoxyeicosatrienoic acids

Arachidonic acid (ARA) is metabolized by cyclooxygenase (COX) and cytochrome P450 to produce proangiogenic metabolites. Specifically, epoxyeicosatrienoic acids (EETs) produced from the P450 pathway are angiogenic, inducing cancer tumor growth. A previous study showed that inhibiting soluble epoxide hydrolase (sEH) increased EET concentration and mildly promoted tumor growth. However, inhibiting both sEH and COX led to a dramatic decrease in tumor growth, suggesting that the contribution of EETs to angiogenesis and subsequent tumor growth may be attributed to downstream metabolites formed by COX. This study explores the fate of EETs with COX, the angiogenic activity of the primary metabolites formed, and their subsequent hydrolysis by sEH and microsomal EH. Three EET regioisomers were found to be substrates for COX, based on oxygen consumption and product formation. EET substrate preference for both COX-1 and COX-2 were estimated as 8,9-EET > 5,6-EET > 11,12-EET, whereas 14,15-EET was inactive. The structure of two major products formed from 8,9-EET in this COX pathway were confirmed by chemical synthesis: ct-8,9-epoxy-11-hydroxy-eicosatrienoic acid (ct-8,9-E-11-HET) and ct-8,9-epoxy-15-hydroxy-eicosatrienoic acid (ct-8,9-E-15-HET). ct-8,9-E-11-HET and ct-8,9-E-15-HET are further metabolized by sEH, with ct-8,9-E-11-HET being hydrolyzed much more slowly. Using an s.c. Matrigel assay, we showed that ct-8,9-E-11-HET is proangiogenic, whereas ct-8,9-E-15-HET is not active. This study identifies a functional link between EETs and COX and identifies ct-8,9-E-11-HET as an angiogenic lipid, suggesting a physiological role for COX metabolites of EETs.

Psychomotor retardation with a 1q42.11-q42.12 deletion

A 1q42 deletion is a rare structure variation that commonly harbours various deletion breakpoints along with diversified phenotypes. In our study, we found a de novo 1q42 deletion in a boy who did not have a cleft palate or a congenital diaphragmatic hernia but presented with psychomotor retardation. A 1.9 Mb deletion located within 1q42.11-q42.12 was validated at the molecular cytogenetic level. This is the first report of a 1q42.11-q42.12 deletion in a patient with onlypsychomotor retardation. The precise break points could facilitate the discovery of potential causative genes, such as LBR, EPHX1, etc. The correlation between the psychomotor retardation and the underlying genetic factors could not only shed light on the diagnosis of psychomotor retardation at the genetic level but also provide potential therapeutic targets.

5,6-δ-DHTL, a stable metabolite of arachidonic acid, is a potential EDHF that mediates microvascular dilation

OBJECTIVE

Prominent among the endothelium-derived hyperpolarizing factors (EDHFs) are the Cytochrome P450 (CYP) epoxygenase-derived arachidonic acid metabolites-the epoxyeicosatrienoic acids (EETs), that are known as vasodilators in the microcirculation. Among the EET isomers, 5,6-EET undergoes rapid lactonization in aqueous solution to the more stable 5,6-δ DHTL (5,6-dihydroxytrienoic lactone) isomer. It is unclear whether this metabolic transformation maintains its vasodilator potential and what is the mechanism of action. Thus, the aim of this study was to investigate the capacity of the lactone isomer, 5,6- δ DHTL, to induce dilation of arterioles and explore the endothelial Ca²⁺ response mechanism.

APPROACH AND RESULTS

In isolated human microvessels 5,6- δ DHTL induced a dose dependent vasodilation, that was inhibited by mechanical denudation of the endothelial layer. This 5,6- δ DHTL -dependent dilation was partially reduced in the presence of L-NAME (NOS inhibitor) or the NO-scavenger, cPTIO (by 19.7%, which was not statistically significantly). In human endothelial cells, 5,6- δ DHTL induced an increase in intracellular Ca²⁺([Ca²⁺]i) in a dose dependent manner. This increase in [Ca²⁺]i was similar to that induced by the 5,6-EET isomer, and significantly higher than observed by administering the hydrolytic dihydroxy isomer, 5,6-DHET. Further experiments aimed to investigate the mechanism of action revealed, that the 5,6-δ DHTL-mediated ([Ca²⁺]i elevation was reduced by IP3 and ryanodine antagonists, but not by antagonists to the TRPV4 membrane channel. Similar to their effect on the dilation response in the arteries, NO inhibitors reduced the 5,6-δ DHTL-mediated ([Ca²⁺]i elevation by 20%. Subsequent 5,6-δ DHTL -dependent K⁺ ion efflux from endothelial cells, was abolished by the inhibition of small and intermediate conductance K_Ca.

CONCLUSIONS

The present study shows that 5,6-δ DHTL is a potential EDHF, that dilates microvessels through a mechanism that involves endothelial dependent Ca²⁺ entry, requiring endothelial hyperpolarization. These results suggest the existence of additional lactone-containing metabolites that can be derived from the PUFA metabolism and which may function as novel EDHFs.

Soluble epoxide hydrolase activity and pharmacologic inhibition in horses with chronic severe laminitis

BACKGROUND

The roles of soluble epoxide hydrolase and lipid mediators in inflammatory and neuropathic pain could be relevant in laminitis pain management.

OBJECTIVES

To determine soluble epoxide hydrolase (sEH) activity in the digital laminae, sEH inhibitor potency in vitro, and efficacy of a sEH inhibitor as an adjunct analgesic therapy in chronic laminitic horses.

STUDY DESIGN

In vitro experiments and clinical case series.

METHODS

sEH activity was measured in digital laminae from euthanised healthy and laminitic horses (n = 5-6/group). Potency of 7 synthetic sEH inhibitors was determined in vitro using equine liver cytosol. One of them (t-TUCB; 0.1 mg/kg bwt i.v. every 24 h) was selected based on potency and stability, and used as adjunct therapy in 10 horses with severe chronic laminitis (Obel grades 2, one horse; 3-4, nine horses). Daily assessments of forelimb lifts, pain scores, physiologic and laboratory examinations were performed before (baseline) and during t-TUCB treatment. Data are presented as mean ± s.d. and 95% confidence intervals (CI).

RESULTS

sEH activity in the digital laminae from laminitic horses (0.9±0.6 nmol/min/mg; 95% CI 0.16-1.55 nmol/min/mg) was significantly greater (P = 0.01) than in healthy horses (0.17±0.09 nmol/min/mg; CI 0.07-0.26 nmol/min/mg). t-TUCB as an adjunct analgesic up to 10 days (4.3±3 days) in laminitic horses was associated with significant reduction in forelimb lifts (36±22%; 95% CI 9-64%) and in pain scores (18±23%; 95% CI 2-35%) compared with baseline (P = 0.04). One horse developed gas colic and another corneal vascularisation in a blind eye during treatment. No other significant changes were observed.

MAIN LIMITATIONS

Absence of control group and evaluator blinding in case series.

CONCLUSIONS

sEH activity is significantly higher in the digital laminae of actively laminitic compared with healthy horses, and use of a potent inhibitor of equine sEH as adjunct analgesic therapy appears to decrease signs of pathologic pain in laminitic horses.

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.

18F-FNDP for PET Imaging of Soluble Epoxide Hydrolase

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme located within cytosol and peroxisomes that converts epoxides to the corresponding diols and hydrolyzes phosphate monoesters. It serves to inactivate epoxyeicosatrienoic acids (EETs), which are generated in the brain to couple neuronal activity and cerebral blood flow in normal and pathologic states. Altered regulation of sEH was observed previously in various neuropathologic disorders including vascular dementia and stroke. Inhibitors of sEH are pursued as agents to mitigate neuronal damage after stroke. We developed N-(3,3-diphenylpropyl)-6-¹⁸F-fluoronicotinamide (¹⁸F-FNDP), which proved highly specific for imaging of sEH in the mouse and nonhuman primate brain with PET.

METHODS

¹⁸F-FNDP was synthesized from the corresponding bromo precursor. sEH inhibitory activity of ¹⁸F-FNDP was measured using an sEH inhibitor screening assay kit. Biodistribution was undertaken in CD-1 mice. Binding specificity was assayed in CD-1 and sEH knock-out mice and Papio anubis (baboon) through pretreatment with an sEH inhibitor to block sEH binding. Dynamic PET imaging with arterial blood sampling was performed in 3 baboons, with regional tracer binding quantified using distribution volume. The metabolism of ¹⁸F-FNDP in baboons was assessed using high-performance liquid chromatography.

RESULTS

¹⁸F-FNDP (inhibition binding affinity constant, 1.73 nM) was prepared in 1 step in a radiochemical yield of 14% ± 7%, specific radioactivity in the range of 888-3,774 GBq/μmol, and a radiochemical purity greater than 99% using an automatic radiosynthesis module. The time of preparation was about 75 min. In CD-1 mice, regional uptake followed the pattern of striatum > cortex > hippocampus > cerebellum, consistent with the known brain distribution of sEH, with 5.2% injected dose per gram of tissue at peak uptake. Blockade of 80%-90% was demonstrated in all brain regions. Minimal radiotracer uptake was present in sEH knock-out mice. PET baboon brain distribution paralleled that seen in mouse, with a marked blockade (95%) noted in all regions indicating sEH-mediated uptake of ¹⁸F-FNDP. Two hydrophilic metabolites were identified, with 20% parent compound present at 90 min after injection in baboon plasma.

CONCLUSION

¹⁸F-FNDP can be synthesized in suitable radiochemical yield and high specific radioactivity and purity. In vivo imaging experiments demonstrated that ¹⁸F-FNDP targeted sEH in murine and nonhuman primate brain specifically. ¹⁸F-FNDP is a promising PET radiotracer likely to be useful for understanding the role of sEH in a variety of conditions affecting the central nervous system.

Dysregulation of soluble epoxide hydrolase and lipidomic profiles in anorexia nervosa

Individuals with anorexia nervosa (AN) restrict eating and become emaciated. They tend to have an aversion to foods rich in fat. Because epoxide hydrolase 2 (EPHX2) was identified as a novel AN susceptibility gene, and because its protein product, soluble epoxide hydrolase (sEH), converts bioactive epoxides of polyunsaturated fatty acid (PUFA) to the corresponding diols, lipidomic and metabolomic targets of EPHX2 were assessed to evaluate the biological functions of EPHX2 and their role in AN. Epoxide substrates of sEH and associated oxylipins were measured in ill AN, recovered AN and gender- and race-matched controls. PUFA and oxylipin markers were tested as potential biomarkers for AN. Oxylipin ratios were calculated as proxy markers of in vivo sEH activity. Several free- and total PUFAs were associated with AN diagnosis and with AN recovery. AN displayed elevated n-3 PUFAs and may differ from controls in PUFA elongation and desaturation processes. Cytochrome P450 pathway oxylipins from arachidonic acid, linoleic acid, alpha-linolenic acid and docosahexaenoic acid PUFAs are associated with AN diagnosis. The diol:epoxide ratios suggest the sEH activity is higher in AN compared with controls. Multivariate analysis illustrates normalization of lipidomic profiles in recovered ANs. EPHX2 influences AN risk through in vivo interaction with dietary PUFAs. PUFA composition and concentrations as well as sEH activity may contribute to the pathogenesis and prognosis of AN. Our data support the involvement of EPHX2-associated lipidomic and oxylipin dysregulations in AN, and reveal their potential as biomarkers to assess responsiveness to future intervention or treatment.

Genetic enhancement of microsomal epoxide hydrolase improves metabolic detoxification but impairs cerebral blood flow regulation

Microsomal epoxide hydrolase (mEH) is a detoxifying enzyme for xenobiotic compounds. Enzymatic activity of mEH can be greatly increased by a point mutation, leading to an E404D amino acid exchange in its catalytic triad. Surprisingly, this variant is not found in any vertebrate species, despite the obvious advantage of accelerated detoxification. We hypothesized that this evolutionary avoidance is due to the fact that the mEH plays a dualistic role in detoxification and control of endogenous vascular signaling molecules. To test this, we generated mEH E404D mice and assessed them for detoxification capacity and vascular dynamics. In liver microsomes from these mice, turnover of the xenobiotic compound phenanthrene-9,10-oxide was four times faster compared to WT liver microsomes, confirming accelerated detoxification. mEH E404D animals also showed faster metabolization of a specific class of endogenous eicosanoids, arachidonic acid-derived epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs). Significantly higher DHETs/EETs ratios were found in mEH E404D liver, urine, plasma, brain and cerebral endothelial cells compared to WT controls, suggesting a broad impact of the mEH mutant on endogenous EETs metabolism. Because EETs are strong vasodilators in cerebral vasculature, hemodynamics were assessed in mEH E404D and WT cerebral cortex and hippocampus using cerebral blood volume (CBV)-based functional magnetic resonance imaging (fMRI). Basal CBV₀ levels were similar between mEH E404D and control mice in both brain areas. But vascular reactivity and vasodilation in response to the vasodilatory drug acetazolamide were reduced in mEH E404D forebrain compared to WT controls by factor 3 and 2.6, respectively. These results demonstrate a critical role for mEH E404D in vasodynamics and suggest that deregulation of endogenous signaling pathways is the undesirable gain of function associated with the E404D variant.

Soluble epoxide hydrolase inhibitor enhances synaptic neurotransmission and plasticity in mouse prefrontal cortex

Background

The soluble epoxide hydrolase (sEH) is an important enzyme chiefly involved in the metabolism of fatty acid signaling molecules termed epoxyeicosatrienoic acids (EETs). sEH inhibition (sEHI) has proven to be protective against experimental cerebral ischemia, and it is emerging as a therapeutic target for prevention and treatment of ischemic stroke. However, the role of sEH on synaptic function in the central nervous system is still largely unknown. This study aimed to test whether sEH C-terminal epoxide hydrolase inhibitor, 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) affects basal synaptic transmission and synaptic plasticity in the prefrontal cortex area (PFC). Whole cell and extracellular recording examined the miniature excitatory postsynaptic currents (mEPSCs) and field excitatory postsynaptic potentials (fEPSPs); Western Blotting determined the protein levels of glutamate receptors and ERK phosphorylation in acute medial PFC slices.

Results

Application of the sEH C-terminal epoxide hydrolase inhibitor, AUDA significantly increased the amplitude of mEPSCs and fEPSPs in prefrontal cortex neurons, while additionally enhancing long term potentiation (LTP). Western Blotting demonstrated that AUDA treatment increased the expression of the N-methyl-D-aspartate receptor (NMDA) subunits NR1, NR2A, NR2B; the α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluR1, GluR2, and ERK phosphorylation.

Conclusions

Inhibition of sEH induced an enhancement of PFC neuronal synaptic neurotransmission. This enhancement of synaptic neurotransmission is associated with an enhanced postsynaptic glutamatergic receptor and postsynaptic glutamatergic receptor mediated synaptic LTP. LTP is enhanced via ERK phosphorylation resulting from the delivery of glutamate receptors into the PFC by post-synapse by treatment with AUDA. These findings provide a possible link between synaptic function and memory processes.

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.

Microsomal epoxide hydrolase 1 (EPHX1): Gene, structure, function, and role in human disease

Microsomal epoxide hydrolase (EPHX1) is an evolutionarily highly conserved biotransformation enzyme for converting epoxides to diols. Notably, the enzyme is able to either detoxify or bioactivate a wide range of substrates. Mutations and polymorphic variants in the EPHX1 gene have been associated with susceptibility to several human diseases including cancer. This review summarizes the key knowledge concerning EPHX1 gene and protein structure, expression pattern and regulation, and substrate specificity. The relevance of EPHX1 for human pathology is especially discussed.

Profiling the Oxylipin and Endocannabinoid Metabolome by UPLC-ESI-MS/MS in Human Plasma to Monitor Postprandial Inflammation

Bioactive lipids, including oxylipins, endocannabinoids, and related compounds may function as specific biochemical markers of certain aspects of inflammation. However, the postprandial responsiveness of these compounds is largely unknown; therefore, changes in the circulating oxylipin and endocannabinoid metabolome in response to a challenge meal were investigated at six occasions in a subject who freely modified her usual diet. The dietary change, and especially the challenge meal itself, represented a modification of precursor fatty acid status, with expectedly subtle effects on bioactive lipid levels. To detect even the slightest alteration, highly sensitive ultra-performance liquid chromatography (UPLC) coupled to electrospray ionization (ESI) tandem mass spectrometry (MS/MS) methods for bioactive lipid profiling was employed. A previously validated UPLC-ESI-MS/MS method for profiling the endocannabinoid metabolome was used, while validation of an UPLC-ESI-MS/MS method for oxylipin analysis was performed with acceptable outcomes for a majority of the parameters according to the US Food and Drug Administration guidelines for linearity (0.9938 < R2 < 0.9996), limit of detection (0.0005-2.1 pg on column), limit of quantification (0.0005-4.2 pg on column), inter- and intraday accuracy (85-115%) and precision (< 5%), recovery (40-109%) and stability (40-105%). Forty-seven of fifty-two bioactive lipids were detected in plasma samples at fasting and in the postprandial state (0.5, 1, and 3 hours after the meal). Multivariate analysis showed a significant shift of bioactive lipid profiles in the postprandial state due to inclusion of dairy products in the diet, which was in line with univariate analysis revealing seven compounds (NAGly, 9-HODE, 13-oxo-ODE, 9(10)-EpOME, 12(13)-EpOME, 20-HETE, and 11,12-DHET) that were significantly different between background diets in the postprandial state (but not at fasting). The only change in baseline levels at fasting was displayed by TXB2. Furthermore, postprandial responsiveness was detected for seven compounds (POEA, SEA, 9(10)-DiHOME, 12(13)-DiHOME, 13-oxo-ODE, 9-HODE, and 13-HODE). Hence, the data confirm that the UPLC-ESI-MS/MS method performance was sufficient to detect i) a shift, in the current case most notably in the postprandial bioactive lipid metabolome, caused by changes in diet and ii) responsiveness to a challenge meal for a subset of the oxylipin and endocannabinoid metabolome. To summarize, we have shown proof-of-concept of our UPLC-ESI-MS/MS bioactive lipid protocols for the purpose of monitoring subtle shifts, and thereby useful to address lipid-mediated postprandial inflammation.

5,6-δ-DHTL, a stable metabolite of arachidonic acid, is a potential substrate for paraoxonase 1

Paraoxonase 1 (PON1) is an antiatherogenic high density lipoprotein-associated lactonase. Recent findings revealed that PON1 knockout mice have low blood pressure, which is negatively correlated with the level of 5,6-epoxyeicosatrienoic acid (5,6-EET), a cytochrome P450 -derived arachidonic acid metabolite. 5,6-EET is an endothelium-derived hyperpolarizing factor that causes arterial dilation. Under physiological conditions, 5,6-EET is unstable, transforming to its δ-lactone (5,6-δ-DHTL) that evades the degradation by soluble epoxide hydrolase (sEH), arguing for the existence of yet another enzyme that is responsible specifically for its hydrolysis. We therefore hypothesized that PON1 degrades the 5,6-δ-DHTL, and this specific PON1 lactonase activity thus decreases endothelial vasodilatation. The aim of the present study was to investigate the PON1-5,6-δ-DHTL relationship. A liquid chromatography mass spectrometry based method for 5,6-EET derivatives identification was developed. Tracking the lactonization of 5,6-EET in a physiological solution revealed that 5,6-EET was fully converted into 5,6-δ-DHTL. Incubation of 5,6-δ-DHTL with rePON1 resulted in 85.1±3.4% degradation of the substrate to 5,6 dihydroxytrienoic acid (5,6-DHET), while only 12.0±8.7% hydrolysis was detected in the absence of PON1. Accordingly, the levels of 5,6-DHTL were found to be significantly higher in the PON1KO mice than in the wild type mice. Kinetic analysis revealed values of Vmax=0.021±0.01μM/s and Km=150.99±62.1μM. Calculation of the docking energy suggested possible interaction of the 5,6-δ-DHTL in the catalytic region of PON1 with free energy of-5.57 Kcal/mol, preferentially for the (S) enantiomer. These findings demonstrate that 5,6-δ-DHTL is a PON1 substrate and imply that the 5,6-EET vasodilation effect may be impaired by PON1.

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.

Soluble epoxide hydrolase activity regulates inflammatory responses and seizure generation in two mouse models of temporal lobe epilepsy

Neuroinflammation is known to be involved in epileptogenesis with unclear mechanisms. Inhibition of soluble epoxide hydrolase (sEH) seems to offer anti-inflammatory protection to ischemic brain injury in rodents. Thus, it is hypothesized that sEH inhibition might also affect the neuroinflammatory responses caused by epileptic seizures. In the present study, we investigated the involvement of sEH in neuroinflammation, seizure generation and subsequent epileptogenesis using two mouse models of temporal lobe epilepsy. Experimental epileptic seizures were induced by either pilocarpine or electrical amygdala kindling in both wild-type (WT) C57BL/6 mice and sEH knockout (sEH KO) mice. The sEH expression in the hippocampus was detected by immunohistochemistry and Western blot analysis. The effects of the sEH hydrolase inhibitors, 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) and N-[1-(1-oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy) phenyl)-urea (TPPU), and of the genetic deletion of sEH on seizure-induced neuroinflammatory responses and the development of epilepsy were evaluated. In the hippocampus of WT mice, sEH was mainly expressed in astrocytes (GFAP(+)), neurons (NeuN(+)) and scattered microglia (Iba-1(+)) in the regions of CA1, CA3 and dentate gyrus. Expression of sEH was significantly increased on day 7, 14, 21 and 28 after pilocarpine-induced status epilepticus (SE). Administration with sEH inhibitors attenuated the SE-induced up-regulation of interleukin-1β (IL-1β) and interleukin-6 (IL-6), the degradation of EETs, as well as IκB phosphorylation. Following treatment with AUDA, the frequency and duration of spontaneous motor seizures in the pilocarpine-SE mice were decreased and the seizure-induction threshold of the fully kindled mice was increased. Up-regulation of hippocampal IL-1β and IL-6 was found in both WT and sEH KO mice after successful induction of SE. Notably, sEH KO mice were more susceptible to seizures than WT mice. Seizure related neuroinflammation and ictogenesis were attenuated by pharmacological inhibition of sEH enzymatic activity but not by sEH genetic deletion. Therefore, sEH may play an important role in the generation of epilepsy. Furthermore, the effectiveness of AUDA in terms of anti-inflammatory and anti-ictogenesis properties suggests that it may have clinical therapeutic implication for epilepsy in the future, particularly when treating temporal lobe epilepsy.

Soluble epoxide hydrolase as an anti-inflammatory target of the thrombolytic stroke drug SMTP-7

Although ischemic stroke is a major cause of death and disability worldwide, only a small fraction of patients benefit from the current thrombolytic therapy due to a risk of cerebral hemorrhage caused by inflammation. Thus, the development of a new strategy to combat inflammation during thrombolysis is an urgent demand. The small molecule thrombolytic SMTP-7 effectively treats ischemic stroke in several animal models with reducing cerebral hemorrhage. Here we revealed that SMTP-7 targeted soluble epoxide hydrolase (sEH) to suppress inflammation. SMTP-7 inhibited both of the two sEH enzyme activities: epoxide hydrolase (which inactivates anti-inflammatory epoxy-fatty acids) and lipid phosphate phosphatase. SMTP-7 suppressed epoxy-fatty acid hydrolysis in HepG2 cells in culture, implicating the sEH inhibition in the anti-inflammatory mechanism. The sEH inhibition by SMTP-7 was independent of its thrombolytic activity. The simultaneous targeting of thrombolysis and sEH by a single molecule is a promising strategy to revolutionize the current stroke therapy.

Post-exposure administration of diazepam combined with soluble epoxide hydrolase inhibition stops seizures and modulates neuroinflammation in a murine model of acute TETS intoxication

Tetramethylenedisulfotetramine (TETS) is a potent convulsant poison for which there is currently no approved antidote. The convulsant action of TETS is thought to be mediated by inhibition of type A gamma-aminobutyric acid receptor (GABAAR) function. We, therefore, investigated the effects of post-exposure administration of diazepam, a GABAAR positive allosteric modulator, on seizure activity, death and neuroinflammation in adult male Swiss mice injected with a lethal dose of TETS (0.15mg/kg, ip). Administration of a high dose of diazepam (5mg/kg, ip) immediately following the second clonic seizure (approximately 20min post-TETS injection) effectively prevented progression to tonic seizures and death. However, this treatment did not prevent persistent reactive astrogliosis and microglial activation, as determined by GFAP and Iba-1 immunoreactivity and microglial cell morphology. Inhibition of soluble epoxide hydrolase (sEH) has been shown to exert potent anti-inflammatory effects and to increase survival in mice intoxicated with other GABAAR antagonists. The sEH inhibitor TUPS (1mg/kg, ip) administered immediately after the second clonic seizure did not protect TETS-intoxicated animals from tonic seizures or death. Combined administration of diazepam (5mg/kg, ip) and TUPS (1mg/kg, ip, starting 1h after diazepam and repeated every 24h) prevented TETS-induced lethality and influenced signs of neuroinflammation in some brain regions. Significantly decreased microglial activation and enhanced reactive astrogliosis were observed in the hippocampus, with no changes in the cortex. Combining an agent that targets specific anti-inflammatory mechanisms with a traditional antiseizure drug may enhance treatment outcome in TETS intoxication.

The role of long chain fatty acids and their epoxide metabolites in nociceptive signaling

Lipid derived mediators contribute to inflammation and the sensing of pain. The contributions of omega-6 derived prostanoids in enhancing inflammation and pain sensation are well known. Less well explored are the opposing anti-inflammatory and analgesic effects of the omega-6 derived epoxyeicosatrienoic acids. Far less has been described about the epoxidized metabolites derived from omega-3 long chain fatty acids. The epoxide metabolites are turned over rapidly with enzymatic hydrolysis by the soluble epoxide hydrolase being the major elimination pathway. Despite this, the overall understanding of the role of lipid mediators in the pathology of chronic pain is growing. Here, we review the role of long chain fatty acids and their metabolites in alleviating both acute and chronic pain conditions. We focus specifically on the epoxidized metabolites of omega-6 and omega-3 long chain fatty acids as well as a novel strategy to modulate their activity in vivo.

Cytochrome P450 epoxygenase pathway of polyunsaturated fatty acid metabolism

Polyunsaturated fatty acids (PUFA) are oxidized by cytochrome P450 epoxygenases to PUFA epoxides which function as potent lipid mediators. The major metabolic pathways of PUFA epoxides are incorporation into phospholipids and hydrolysis to the corresponding PUFA diols by soluble epoxide hydrolase. Inhibitors of soluble epoxide hydrolase stabilize PUFA epoxides and potentiate their functional effects. The epoxyeicosatrienoic acids (EETs) synthesized from arachidonic acid produce vasodilation, stimulate angiogenesis, have anti-inflammatory actions, and protect the heart against ischemia-reperfusion injury. EETs produce these functional effects by activating receptor-mediated signaling pathways and ion channels. The epoxyeicosatetraenoic acids synthesized from eicosapentaenoic acid and epoxydocosapentaenoic acids synthesized from docosahexaenoic acid are potent inhibitors of cardiac arrhythmias. Epoxydocosapentaenoic acids also inhibit angiogenesis, decrease inflammatory and neuropathic pain, and reduce tumor metastasis. These findings indicate that a number of the beneficial functions of PUFA may be due to their conversion to PUFA epoxides. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Mechanism of the sex difference in endothelial dysfunction after stroke

Stroke, the number four cause of death in the United States, is a greatly debilitating event resulting from insufficient blood supply to the brain (cerebral ischemia). Endothelial dysfunction, primarily characterized by dampened endothelial- dependent vasodilation, is a major contributor to the development and outcome of stroke. This review discusses the role of soluble epoxide hydrolase (sEH), an enzyme responsible for the degradation of vasoprotective eicosatrienoic acids (EETs), in the context of the cerebral vasculature and its contribution to the sexual dimorphic nature of stroke.

Role of soluble epoxide hydrolase in exacerbation of stroke by streptozotocin-induced type 1 diabetes mellitus

Hyperglycemia worsens stroke, yet rigorous glycemic control does not improve neurologic outcome. An alternative is to target downstream molecular mediator(s) triggered by hyperglycemia but independent of prevailing glycemia. Soluble epoxide hydrolase (sEH) is a potential mediator of injury via its metabolism of neuroprotective epoxyeicosatrienoic acids (EETs). We tested whether hyperglycemia exacerbates cerebral injury by upregulating sEH and decreasing brain EET levels. Type 1 diabetes mellitus was modeled by streptozotocin (STZ; 50 mg/kg per day intraperitoneally, 5 days) in male mice. At 4 weeks, STZ-treated and control mice underwent 45-minute middle cerebral artery occlusion (MCAO) with or without sEH blockade by trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB; 1 mg/kg intraperitoneally daily for 6 days before MCAO). The STZ-treated mice had increased sEH mRNA expression in cerebral vessels and decreased EET concentrations in brain. There was no difference in cortical perfusion between groups. The STZ-treated mice sustained larger brain infarct than controls. Pretreatment with t-AUCB eliminated the difference in infarct size and EETs concentration between STZ-treated mice and controls, without altering glycemia. We conclude that type 1 diabetes mellitus upregulates sEH mRNA and decreases concentrations of neuroprotective EETs within the brain, leading to worse stroke outcome. The data indicate that sEH antagonism may be beneficial in the setting of hyperglycemic stroke.

Developmental changes in the transcriptome of the rat choroid plexus in relation to neuroprotection

Background

The choroid plexuses are the interface between the blood and the cerebrospinal fluid (CSF) contained within the ventricular spaces of the central nervous system. The tight junctions linking adjacent cells of the choroidal epithelium create a physical barrier to paracellular movement of molecules. Multispecific efflux transporters as well as drug-metabolizing and antioxidant enzymes functioning in these cells contribute to a metabolic barrier. These barrier properties reflect a neuroprotective function of the choroid plexus. The choroid plexuses develop early during embryogenesis and provide pivotal control of the internal environment throughout development when the brain is especially vulnerable to toxic insults. Perinatal injuries like hypoxia and trauma, and exposure to drugs or toxic xenobiotics can have serious consequences on neurogenesis and long-term development. The present study describes the developmental expression pattern of genes involved in the neuroprotective functions of the blood–CSF barrier.

Methods

The transcriptome of rat lateral ventricular choroid plexuses isolated from fifteen-day-old embryos, nineteen-day old fetuses, two-day old pups, and adults was analyzed by a combination of Affymetrix microarrays, Illumina RNA-Sequencing, and quantitative RT-PCR.

Results

Genes coding for proteins involved in junction formation are expressed early during development. Overall perinatal expression levels of genes involved in drug metabolism and antioxidant mechanisms are similar to, or higher than levels measured in adults. A similar developmental pattern was observed for multispecific efflux transporter genes of the Abc and Slc superfamilies. Expression of all these genes was more variable in choroid plexus from fifteen-day-old embryos. A large panel of transcription factors involved in the xenobiotic- or cell stress-mediated induction of detoxifying enzymes and transporters is also expressed throughout development.

Conclusions

This transcriptomic analysis suggests relatively well–established neuroprotective mechanisms at the blood-CSF barrier throughout development of the rat. The expression of many transcription factors early in development raises the possibility of additional protection for the vulnerable developing brain, should the fetus or newborn be exposed to drugs or other xenobiotics.

Effects of AS2586114, a soluble epoxide hydrolase inhibitor, on hyperlocomotion and prepulse inhibition deficits in mice after administration of phencyclidine

Accumulating evidence suggests that soluble epoxide hydrolase (sEH) plays a key role in controlling levels of lipid signaling molecules, and that the potent sEH inhibitors may be potential therapeutic drugs for a number of diseases associated with metabolism of epoxyeicosatrienoic acids (EETs). This study was undertaken to examine whether the potent sEH inhibitor AS2586114 could attenuate behavioral abnormalities (e.g., hyperlocomotion and prepulse inhibition (PPI) deficits) in male ddY mice after a single administration of the N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (PCP). A single oral administration of AS2586114 (10, 30, or 100 mg/kg) attenuated the hyperlocomotion in mice after the administration of PCP (3.0 mg/kg, s.c.), in a dose dependent manner. Furthermore, a single oral administration of AS2586114 (10, 30, or 100 mg/kg) improved the PPI deficits in mice after the administration of PCP (3.0 mg/kg, s.c.), in a dose dependent manner. In addition, the atypical antipsychotic drug clozapine (10 mg/kg, p.o.) significantly attenuated hyperlocomotion and PPI deficits after the administration of PCP (3.0 mg/kg, s.c.). In conclusion, this study suggests that AS2586114 may have antipsychotic activity in PCP models of schizophrenia. Therefore, it is likely that the sEH inhibitors may be potential therapeutic drugs for neuropsychiatric diseases such as schizophrenia.

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.

A systems biology approach to identify the signalling network regulated by Rho-GDI-γ during neural stem cell differentiation

Understanding the molecular mechanism that underlies the differentiation of neural stem cells (NSCs) is vital to develop regenerative medicines for neurological disorders. In our previous work, Rho-GDI-γ was found to be able to prompt neuronal differentiation when it was down regulated. However, it is unclear how Rho-GDI-γ regulates this differentiation process. Therefore, a novel systems biology approach is presented here to identify putative signalling pathways regulated by Rho-GDI-γ during NSC differentiation, and these pathways can provide insights into the NSC differentiation mechanisms. In particular, our proposed approach combines the predictive power of computational biology and molecular experiments. With different biological experiments, the genes in the computationally identified signalling network were validated to be indeed regulated by Rho-GDI-γ during the differentiation of NSCs. In particular, one randomly selected pathway involving Vcp, Mapk8, Ywhae and Ywhah was experimentally verified to be regulated by Rho-GDI-γ. These promising results demonstrate the effectiveness of our proposed systems biology approach, indicating the potential predictive power of integrating computational and experimental approaches.

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.

Altered behavioral phenotypes in soluble epoxide hydrolase knockout mice: effects of traumatic brain injury

After traumatic brain injury (TBI), arachidonic acid (ArA) is released from damaged cell membranes and metabolized to many bioactive eicosanoids, including several epoxyeicosatrienoic acids (EETs). Soluble epoxide hydrolase (Ephx2, sEH) appears to be the predominant pathway for EET metabolism to less active dihydroxyeicosatrienoates (DHETs). Prior studies indicate that brain levels of EETs increase transiently after TBI and EETs have antiinflammatory and neuroprotective activities which may benefit the injured brain. If the net effect of increased EET levels in the injured brain is beneficial to recovery, then Ephx2 gene disruption would be expected to enhance elevated EET levels and improve recovery in the injured brain. Thus, Ephx2-KO (Ephx2(-/-) bred onto pure C57Bl/6 background) mice were compared to wild-type controls in a unilateral controlled cortical impact model of TBI. Before injury, animals behaved comparably in open field activity and neurologic reflexes. Interestingly, the Ephx2-KO mice showed improved motor coordination on a beam walk task, yet showed indications of defective learning in a test of working spatial memory. After surgery, brain-injured Ephx2-KO mice again had less of a deficit in the beam walk than wild-type, and the difference in latency (post-pre) showed a trend of protection for Ephx2-KO mice after TBI. Brain-injured mice showed no genotype differences in working memory. Surprisingly, sham-operated Ephx2-KO mice exhibited an injured phenotype for working memory, compared to sham-operated wild-type mice. Brain eicosanoid levels were measured using liquid chromatography with tandem mass spectrometry. Of the 20 eicosanoids evaluated, only 8,9-EET was elevated in the Ephx2-KO cerebral cortex (37 d post-surgery, in both sham and injured). Tissue DHET levels were below the limit of quantification. These results reflect a significant contribution of sEH deficiency in coordination of ambulatory movements and working spatial memory in the mouse. Further investigation of differential sEH expression and EET levels at earlier time points and across other brain regions may shed light on these behavioral differences.

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.

Soluble epoxide hydrolase inhibition, epoxygenated fatty acids and nociception

The soluble epoxide hydrolase (sEH) enzyme regulates the levels of endogenous epoxygenated fatty acid (EFA) lipid metabolites by rapidly degrading these molecules. The EFAs have pleiotropic biological activities including the modulation of nociceptive signaling. Recent findings indicate that the EFAs, in particular the arachidonic acid (AA) derived epoxyeicosatrienoic acids (EETs), the docosahexaenoic acid (DHA) derived epoxydocosapentaenoic acids (EpDPEs) and eicosapentaenoic acid (EPA) derived epoxyeicosatetraenoic acids (EpETEs) are natural signaling molecules. The tight regulation of these metabolites speaks to their importance in regulating biological functions. In the past several years work on EFAs in regard to their activities in the nervous system evolved to demonstrate that these molecules are anti-inflammatory and anti-nociceptive. Here we focus on the recent advances in understanding the effects of sEH inhibition and increased EFAs on the nociceptive system and their ability to reduce pain. Evidence of their role in modulating pain signaling is given by their direct application and by inhibiting their degradation in various models of pain. Moreover, there is mounting evidence of EFAs role in the crosstalk between major nociceptive and anti-nociceptive systems which is reviewed herein. Overall the fundamental knowledge generated within the past decade indicates that orally bioavailable small molecule inhibitors of sEH may find a place in the treatment of a number of diverse painful conditions including inflammatory and neuropathic pain.

Development of fluorescent substrates for microsomal epoxide hydrolase and application to inhibition studies

The microsomal epoxide hydrolase (mEH) plays a significant role in the metabolism of numerous xenobiotics. In addition, it has a potential role in sexual development and bile acid transport, and it is associated with a number of diseases such as emphysema, spontaneous abortion, eclampsia, and several forms of cancer. Toward developing chemical tools to study the biological role of mEH, we designed and synthesized a series of absorbent and fluorescent substrates. The highest activity for both rat and human mEH was obtained with the fluorescent substrate cyano(6-methoxy-naphthalen-2-yl)methyl glycidyl carbonate (11). An in vitro inhibition assay using this substrate ranked a series of known inhibitors similarly to the assay that used radioactive cis-stilbene oxide but with a greater discrimination between inhibitors. These results demonstrate that the new fluorescence-based assay is a useful tool for the discovery of structure-activity relationships among mEH inhibitors. Furthermore, this substrate could also be used for the screening chemical library with high accuracy and with a Z' value of approximately 0.7. This new assay permits a significant decrease in labor and cost and also offers the advantage of a continuous readout. However, it should not be used with crude enzyme preparations due to interfering reactions.

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.