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

Inhibiting Soluble Epoxide Hydrolase Suppresses NF-κB p65 Signaling and Reduces CXCL10 Expression as a Potential Therapeutic Target in Hashimoto's Thyroiditis

BACKGROUND

Although Hashimoto's thyroiditis (HT) is one of most common autoimmune thyroid diseases, its treatment remains focused on symptom relief. The soluble epoxide hydrolase (sEH) shows potential functions as a drug target in alleviating some autoimmune diseases; however, we seldom know its role in HT.

METHODS

The protein expression of sEH and related downstream molecules were evaluated by immunohistochemistry, Western blotting, ELISA, or immunofluorescence staining. RNA sequencing of tissue samples was performed to analyze differential genes and dysregulated pathways in HT and controls. The thyroid follicular epithelial cells (TFECs) and rat HT model were used to verify the biological function of sEH and the inhibition role of adamantyl-ureido-dodecanoic acid (AUDA) in HT.

RESULTS

The sEH was significantly upregulated in HT patients compared with healthy individuals. Transcriptome sequencing showed cytokine-related pathways and chemokine expression; especially chemokine CXCL10 and its receptor CXCR3 were aberrant in HT patients. In TFECs and a rat HT model, blocking sEH by AUDA inhibitor could effectively inhibit the autoantibody, proinflammatory nuclear kappa factor B (NF-κB) signaling, chemokine CXCL10/CXCR3 expression, and type-1 helper CD4+ T cells.

CONCLUSION

Our findings suggest that sEH/NF-κB p65/CXCL10-CXCR3 might be promising therapeutic targets for HT.

A Narrative Review of the Published Pre-Clinical Evaluations: Multiple Effects of Arachidonic Acid, its Metabolic Enzymes and Metabolites in Epilepsy

Arachidonic acid (AA), an important polyunsaturated fatty acid in the brain, is hydrolyzed by a direct action of phospholipase A2 (PLA2) or through the combined action of phospholipase C and diacylglycerol lipase, and released into the cytoplasm. Various derivatives of AA can be synthesized mainly through the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (P450) enzyme pathways. AA and its metabolic enzymes and metabolites play important roles in a variety of neurophysiological activities. The abnormal metabolites and their catalytic enzymes in the AA cascade are related to the pathogenesis of various central nervous system (CNS) diseases, including epilepsy. Here, we systematically reviewed literatures in PubMed about the latest randomized controlled trials, animal studies and clinical studies concerning the known features of AA, its metabolic enzymes and metabolites, and their roles in epilepsy. The exclusion criteria include non-original studies and articles not in English.

Soluble epoxide hydrolase inhibitor (TPPU) alleviates ferroptosis by regulating CCL5 after intracerebral hemorrhage in mice

Soluble epoxide hydrolase (sEH) inhibition has been shown multiple beneficial effects against brain injuries of Intracerebral hemorrhage (ICH). However, the underlying mechanism of its neuroprotective effects after ICH has not been explained fully. Ferroptosis, a new form of iron-dependent programmed cell death, has been shown to be implicated in the secondary injuries after ICH. In this study, We examined whether sEH inhibition can alleviate brain injuries of ICH through inhibiting ferroptosis. Expression of several markers for ferroptosis was observed in the peri-hematomal brain tissues in mice after ICH. lip-1, a ferroptosis inhibitor, alleviated iron accumulation, lipid peroxidation and the secondary damages post-ICH in mice model. Intraperitoneal injection of 1-Trifluoromethoxyphenyl-3- (1-propionylpiperidin-4-yl)urea (TPPU), a highly selective sEH inhibitor, could inhibit ferroptosis and alleviate brain damages in ICH mice. Furthermore, RNA-sequencing was applied to explore the potential regulatory mechanism underlying the effects of TPPU in ferroptosis after ICH. C-C chemokine ligand 5 (CCL5) may be the key factor by which TPPU regulated ferroptosis after ICH since CCL5 antagonist could mimic the effects of TPPU and CCL5 reversed the inhibitive effect of TPPU on ferroptosis and the neuroprotective effects of TPPU on secondary damage after ICH. Taken together, these data indicate that ferroptosis is a key pathological feature of ICH and Soluble epoxide hydrolase inhibitor can exert neuroprotective effect by preventing ferroptosis after ICH.

[18F]FNDP PET neuroimaging test-retest repeatability and whole-body dosimetry in humans

PURPOSE

Soluble epoxide hydrolase (sEH) is an enzyme that shapes immune signaling through its role in maintaining the homeostasis of polyunsaturated fatty acids and their related byproducts. [18F]FNDP is a radiotracer developed for use with positron emission tomography (PET) to image sEH, which has been applied to imaging sEH in the brains of healthy individuals. Here, we report the test-retest repeatability of [18F]FNDP brain PET binding and [18F]FNDP whole-body dosimetry in healthy individuals.

METHODS

Seven healthy adults (4 men, 3 women, ages 40.1 ± 4.6 years) completed [18F]FNDP brain PET on two occasions within a period of 14 days in a test-retest study design. [18F]FNDP regional total distribution volume (VT) values were derived from modeling time-activity data with a metabolite-corrected arterial input function. Test-retest variability, mean absolute deviation, and intraclass correlation coefficient (ICC) were investigated. Six other healthy adults (3 men, 3 women, ages 46.0 ± 7.0 years) underwent [18F]FNDP PET/CT for whole-body dosimetry, which was acquired over 4.5 h, starting immediately after radiotracer administration. Organ-absorbed doses and the effective dose were then estimated.

RESULTS

The mean test-retest difference in regional VT (ΔVT) was 0.82 ± 5.17%. The mean absolute difference in regional VT was 4.01 ± 3.33%. The ICC across different brain regions ranged from 0.92 to 0.99. The organs with the greatest radiation-absorbed doses included the gallbladder (0.081 ± 0.024 mSv/MBq), followed by liver (0.077 ± 0.018 mSv/MBq) and kidneys (0.063 ± 0.006 mSv/MBq). The effective dose was 0.020 ± 0.003 mSv/MBq.

CONCLUSION

These data support a favorable test-retest repeatability of [18F]FNDP brain PET regional VT. The radiation dose to humans from each [18F]FNDP PET scan is similar to that of other 18F-based PET radiotracers.

Novel thiazolopyridine derivatives of diflapolin as dual sEH/FLAP inhibitors with improved solubility

Inflammatory responses are orchestrated by a plethora of lipid mediators, and perturbations of their biosynthesis or degradation hinder resolution and lead to uncontrolled inflammation, which contributes to diverse pathologies. Small molecules that induce a switch from pro-inflammatory to anti-inflammatory lipid mediators are considered valuable for the treatment of chronic inflammatory diseases. Commonly used non-steroidal anti-inflammatory drugs (NSAIDs) are afflicted with side effects caused by the inhibition of beneficial prostanoid formation and redirection of arachidonic acid (AA) into alternative pathways. Multi-target inhibitors like diflapolin, the first dual inhibitor of soluble epoxide hydrolase (sEH) and 5-lipoxygenase-activating protein (FLAP), promise improved efficacy and safety but are confronted by poor solubility and bioavailability. Four series of derivatives bearing isomeric thiazolopyridines as bioisosteric replacement of the benzothiazole core and two series additionally containing mono- or diaza-isosteres of the phenylene spacer were designed and synthesized to improve solubility. The combination of thiazolo[5,4-b]pyridine, a pyridinylen spacer and a 3,5-Cl2-substituted terminal phenyl ring (46a) enhances solubility and FLAP antagonism, while preserving sEH inhibition. Moreover, the thiazolo[4,5-c]pyridine derivative 41b, although being a less potent sEH/FLAP inhibitor, additionally decreases thromboxane production in activated human peripheral blood mononuclear cells. We conclude that the introduction of nitrogen, depending on the position, not only enhances solubility and FLAP antagonism (46a), but also represents a valid strategy to expand the scope of application towards inhibition of thromboxane biosynthesis.

Epoxyeicosatrienoic acids and soluble epoxide hydrolase in physiology and diseases of the central nervous system

Epoxyeicosatrienoic acids (EETs) are fatty acid signaling molecules synthesized by cytochrome P450 epoxygenases from arachidonic acid. The biological activity of EETs is terminated when being metabolized by soluble epoxide hydrolase (sEH), a process that serves as a key regulator of tissue EETs levels. EETs act through several signaling pathways to mediate various beneficial effects, including anti-inflammation, anti-apoptosis, and anti-oxidation with relieve of endoplasmic reticulum stress, thereby sEH has become a potential therapeutic target in cardiovascular disease and cancer therapy. Enzymes for EET biosynthesis and metabolism are both widely detected in both neuron and glial cells in the central nervous system (CNS). Recent studies discovered that astrocyte-derived EETs not only mediate neurovascular coupling and neuronal excitability by maintaining glutamate homeostasis but also glia-dependent neuroprotection. Genetic ablation as well as pharmacologic inhibition of sEH has greatly helped to elucidate the physiologic actions of EETs, and maintaining or elevating brain EETs level has been demonstrated beneficial effects in CNS disease models. Here, we review the literature regarding the studies on the bioactivity of EETs and their metabolic enzyme sEH with special attention paid to their action mechanisms in the CNS, including their modulation of neuronal activity, attenuation of neuroinflammation, regulation of cerebral blood flow, and improvement of neuronal and glial cells survival. We further reviewed the recent advance on the potential application of sEH inhibition for treating cerebrovascular disease, epilepsy, and pain disorder.

Soluble epoxide hydrolase inhibitor attenuates BBB disruption and neuroinflammation after intracerebral hemorrhage in mice

Intracerebral hemorrhage (ICH) is a devastating disease with high mortality and morbidity. Soluble epoxide hydrolase (sEH) is the key enzyme in the epoxyeicosatrienoic acids (EETs) signaling. sEH inhibition has been demonstrated to have neuroprotective effects against multiple brain injuries. However, its role in the secondary injuries after ICH has not been fully elucidated. Here we tested the hypothesis that 1-Trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea (TPPU), a potent and highly selective sEH inhibitor, suppresses inflammation and the secondary injuries after ICH. Adult male C57BL/6 mice were subjected to a collagenase-induced ICH model. TPPU alleviated blood-brain barrier damage, inhibited inflammatory response, increased M2 polarization of microglial cells, reduced the infiltration of peripheral neutrophils. In addition, TPPU attenuated neuronal injury and promoted functional recovery. The results suggest that sEH may represent a potential therapeutic target for the treatment of ICH.

First-in-human neuroimaging of soluble epoxide hydrolase using [18F]FNDP PET

PURPOSE

Soluble epoxide hydrolase (sEH) is an enzyme with putative effect on neuroinflammation through its influence on the homeostasis of polyunsaturated fatty acids and related byproducts. sEH is an enzyme that metabolizes anti-inflammatory epoxy fatty acids to the corresponding, relatively inert 1,2-diols. A high availability or activity of sEH promotes vasoconstriction and inflammation in local tissues that may be linked to neuropsychiatric diseases. We developed [¹⁸F]FNDP to study sEH in vivo with positron emission tomography (PET).

METHODS

Brain PET using bolus injection of [¹⁸F]FNDP followed by emission imaging lasting 90 or 180 min was completed in healthy adults (5 males, 2 females, ages 40-53 years). The kinetic behavior of [¹⁸F]FNDP was evaluated using a radiometabolite-corrected arterial plasma input function with compartmental or graphical modeling approaches.

RESULTS

[¹⁸F]FNDP PET was without adverse effects. Akaike information criterion favored the two-tissue compartment model (2TCM) in all ten regions of interest. Regional total distribution volume (V_T) values from each compartmental model and Logan analysis were generally well identified except for corpus callosum V_T using the 2TCM. Logan analysis was assessed as the choice model due to stability of regional V_T values from 90-min data and due to high correlation of Logan-derived regional V_T values with those from the 2TCM. [¹⁸F]FNDP binding was higher in human cerebellar cortex and thalamus relative to supratentorial cortical regions, which aligns with reported expression patterns of the epoxide hydrolase 2 gene in human brain.

CONCLUSION

These data support further use of [¹⁸F]FNDP PET to study sEH in human brain.

Effects of anterior thalamic nuclei stimulation on gene expression in a rat model of temporal lobe epilepsy

Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) has been shown to be effective and safe in the long-term treatment of refractory epilepsy. However, the mechanisms by which ANT-DBS controls epilepsy at the gene expression level (e.g., which regulatory mechanisms are altered) is not well understood. Nine rats were randomly assigned to the control group, the kainic acid (KA) group, and the DBS group. Temporal lobe epilepsy in rats was induced by a stereotaxic KA injection (KA group). The DBS group received the KA injection followed by treatment with ANT-DBS. Video-electroencephalogram (EEG) was used to monitor seizures. Total RNA samples were isolated from the hippocampus of three groups. Microarray was used to detect differentially regulated mRNAs. GO and pathway analysis were performed to analyze the functional categories and affected pathways. qPCR was used to prove the reliability of the microarray results. The differentially expressed genes the KA group and the DBS group, relative to the control group, were screened and a total of 2910 genes were identified. These genes were involved in functional categories such as ion channel activity (P = 5.01 × 10^-8), gated channel activity (P = 1.42 × 10^-7), lipid binding (P = 4.97 × 10^-5), and hydrolase activity (P = 5.02 × 10^-5) and pathways such as calcium signaling pathway (P = 2.09 × 10^-8), glutamatergic synapse (P = 4.09 × 10^-8) and NOD-like receptor signaling pathway (P = 2.70 × 10^-6). Differentially expressed mRNAs might play a role in the pathogenesis of temporal lobe epilepsy. Calcium signaling pathways, synaptic glutamate, and NOD-like receptor signaling pathway play a central role in normal-epilepsy-ANT-DBS treatment series. ANT-DBS achieves its antiepileptic effects by modulating target genes involved in a variety of functions and pathways.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

Soluble Epoxide Hydrolase Inhibition to Face Neuroinflammation in Parkinson's Disease: A New Therapeutic Strategy

Neuroinflammation is a crucial process associated with the pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Several pieces of evidence suggest an active role of lipid mediators, especially epoxy-fatty acids (EpFAs), in the genesis and control of neuroinflammation; 14,15-epoxyeicosatrienoic acid (14,15-EET) is one of the most commonly studied EpFAs, with anti-inflammatory properties. Soluble epoxide hydrolase (sEH) is implicated in the hydrolysis of 14,15-EET to its corresponding diol, which lacks anti-inflammatory properties. Preventing EET degradation thus increases its concentration in the brain through sEH inhibition, which represents a novel pharmacological approach to foster the reduction of neuroinflammation and by end neurodegeneration. Recently, it has been shown that sEH levels increase in brains of PD patients. Moreover, the pharmacological inhibition of the hydrolase domain of the enzyme or the use of sEH knockout mice reduced the deleterious effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. This paper overviews the knowledge of sEH and EETs in PD and the importance of blocking its hydrolytic activity, degrading EETs in PD physiopathology. We focus on imperative neuroinflammation participation in the neurodegenerative process in PD and the putative therapeutic role for sEH inhibitors. In this review, we also describe highlights in the general knowledge of the role of sEH in the central nervous system (CNS) and its participation in neurodegeneration. We conclude that sEH is one of the most promising therapeutic strategies for PD and other neurodegenerative diseases with chronic inflammation process, providing new insights into the crucial role of sEH in PD pathophysiology as well as a singular opportunity for drug development.

Cytochrome P450 derived epoxidized fatty acids as a therapeutic tool against neuroinflammatory diseases

Cytochrome P450 (CYP) metabolism of arachidonic acid (ARA) produces epoxy fatty acids (EpFAs) such as epoxyeicosatrienoic acids (EETs) that are known to exert protective effects in inflammatory disorders. Endogenous EpFAs are further metabolized into corresponding diols by the soluble epoxide hydrolase (sEH). Through inhibition of sEH, many studies have demonstrated the cardioprotective and renoprotective effects of EpFAs; however, the role of sEH inhibition in modulating the pathogenesis of neuroinflammatory disorders is less well described. In this review, we discuss the current knowledge surrounding the effects of sEH inhibition and EpFA action in neuroinflammatory disorders such as Parkinson's Disease (PD), stroke, depression, epilepsy, and Alzheimer's Disease (AD), as well as the potential mechanisms that underlie the therapeutic effects of sEH inhibition.

Genetic deletion of soluble epoxide hydrolase delays the progression of Alzheimer's disease

Background

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with COOH-terminal hydrolase and NH2-terminal lipid phosphatase activities. It is expressed in various cell types in the brain and is involved in the pathogenesis of inflammatory and neurodegenerative diseases. Alzheimer’s disease (AD) is a progressive neuroinflammatory and neurodegenerative disease. However, the pathological significance of sEH and underlying molecular mechanism in AD remain unclear.

Methods

To examine the role of sEH in pathogenesis of AD, we used wild-type (WT) mice, soluble epoxide hydrolase deficient (sEH^−/−) and two mouse models of AD, including amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (APP/PS1 Tg) and APP/PS1 Tg/sEH^−/− mice. Western blotting analysis and immunohistochemistry assay were performed to evaluate the protein expression. Locomotion, nesting building ability, Y-maze, and Morris water maze tests were conducted to study mouse behavior. The levels of interleukin (IL)-1β, IL-4, IL-6, and IL-10 and the activities of NF-κB and nuclear factor of activated T cells (NFAT) were measured by commercial assay kits. The quantitative protein level profiling in the brain lysate was analyzed using LC-MS/MS approaches.

Results

We demonstrated that the level of sEH was increased in the brain and predominantly appeared in hippocampal astrocytes of APP/PS1 Tg mice. Genetic ablation of sEH in APP/PS1 Tg mice delayed the progression of AD as evidenced by the alleviation in behavior outcomes and Aβ plaque deposition. In addition, loss of the function of sEH in APP/PS1 Tg mice increased astrogliosis and the production of astrocyte-derived anti-inflammatory cytokines including IL-1β, IL-4, and IL-10, as well as the activity of NF-kB and NFAT. Moreover, analysis of gene ontology in the AD brain revealed that important signaling pathways and processes related to AD pathogenesis such as translational regulation, oxidative stress, cytoskeleton reorganization, and small GTPase signal transduction were altered in APP/PS1 Tg/sEH^−/− mice compared with APP/PS1 Tg mice.

Conclusion

Our results suggest that sEH is a crucial regulator in the progression of AD and might be a potential therapeutic target for the treatment of AD.

Oxidized Lipids in Persistent Pain States

Chemotherapy, nerve injuries, or diseases like multiple sclerosis can cause pathophysiological processes of persistent and neuropathic pain. Thereby, the activation threshold of ion channels is reduced in peripheral sensory neurons to normally noxious stimuli like heat, cold, acid, or mechanical due to sensitization processes. This leads to enhanced neuronal activity, which can result in mechanical allodynia, cold allodynia, thermal hyperalgesia, spontaneous pain, and may initiate persistent and neuropathic pain. The treatment options for persistent and neuropathic pain patients are limited; for about 50% of them, current medication is not efficient due to severe side effects or low response to the treatment. Therefore, it is of special interest to find additional treatment strategies. One approach is the control of neuronal sensitization processes. Herein, signaling lipids are crucial mediators and play an important role during the onset and maintenance of pain. As preclinical studies demonstrate, lipids may act as endogenous ligands or may sensitize transient receptor potential (TRP)-channels. Likewise, they can cause enhanced activity of sensory neurons by mechanisms involving G-protein coupled receptors and activation of intracellular protein kinases. In this regard, oxidized metabolites of the essential fatty acid linoleic acid, 9- and 13-hydroxyoctadecadienoic acid (HODE), their dihydroxy-metabolites (DiHOMEs), as well as epoxides of linoleic acid (EpOMEs) and of arachidonic acid (EETs), as well as lysophospholipids, sphingolipids, and specialized pro-resolving mediators (SPMs) have been reported to play distinct roles in pain transmission or inhibition. Here, we discuss the underlying molecular mechanisms of the oxidized linoleic acid metabolites and eicosanoids. Furthermore, we critically evaluate their role as potential targets for the development of novel analgesics and for the treatment of persistent or neuropathic pain.

Anti-inflammatory treatment with a soluble epoxide hydrolase inhibitor attenuates seizures and epilepsy-associated depression in the LiCl-pilocarpine post-status epilepticus rat model

PURPOSE

This study aimed to investigate whether 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), a soluble epoxide hydrolase inhibitor with anti-inflammatory effects, could alleviate spontaneous recurrent seizures (SRS) and epilepsy-associated depressive behaviours in the lithium chloride (LiCl)-pilocarpine-induced post-status epilepticus (SE) rat model.

METHODS

The rats were intraperitoneally (IP) injected with LiCl (127 mg/kg) and pilocarpine (40 mg/kg) to induce SE. A video surveillance system was used to monitor SRS in the post-SE model for 6 weeks (from the onset of the 2nd week to the end of the 7th week after SE induction). TPPU (0.1 mg/kg/d) was intragastrically given for 4 weeks from the 21st day after SE induction in the SRS + 0.1 TPPU group. The SRS + PEG 400 group was given the vehicle (40% polyethylene glycol 400) instead, and the control group was given LiCl and PEG 400 but not pilocarpine. The sucrose preference test (SPT) and forced swim test (FST) were conducted to evaluate the depression-like behaviours of rats. Immunofluorescent staining, enzyme-linked immunosorbent assay, and western blot analysis were performed to measure astrocytic and microglial gliosis, neuronal loss, and levels of soluble epoxide hydrolase (sEH), cytokines [tumour necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6], and cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB).

RESULTS

The frequency of SRS was significantly decreased at 6 weeks and 7 weeks after SE induction in the 0.1TPP U group compared with the SRS + PEG 400 group. The immobility time (IMT) evaluated by FST was significantly decreased, whereas the climbing time (CMT) was increased, and the sucrose preference rate (SPR) evaluated by SPT was in an increasing trend. The levels of sEH, TNF-α, IL-1β, and IL-6 in the hippocampus (Hip) and prefrontal cortex (PFC) were all significantly increased in the SRS + PEG 400 group compared with the control group; neuronal loss, astrogliosis, and microglial activation were also observed. The astrocytic and microglial activation and levels of the pro-inflammatory cytokines in the Hip and PFC were significantly attenuated in the TPPU group compared with the SRS + PEG 400 group; moreover, neuronal loss and the decreased CREB expression were significantly alleviated as well.

CONCLUSION

TPPU treatment after SE attenuates SRS and epilepsy-associated depressive behaviours in the LiCl-pilocarpine induced post-SE rat model, and it also exerts anti-inflammatory effects in the brain. Our findings suggest a new therapeutic approach for epilepsy and its comorbidities, especially depression.

Soluble epoxide hydrolase modulates immune responses in activated astrocytes involving regulation of STAT3 activity

BACKGROUND

Astrocyte activation is a common pathological feature in many brain diseases with neuroinflammation, and revealing the underlying mechanisms might shed light on the regulatory processes of the diseases. Recently, soluble epoxide hydrolase (sEH) has been proposed to affect neuroinflammation in brain injuries. However, the roles of astrocytic sEH in brains with neurodegeneration remain unclear.

METHODS

The expression of astrocytic sEH in the brains of APPswe/PSEN1dE9 (APP/PS1) mice developing Alzheimer's disease (AD)-like pathology was evaluated by confocal imaging. LPS-activated primary astrocytes with mRNA silencing or overexpression of sEH were used to investigate its regulatory roles in astrocyte activation and the induction of pro-inflammatory markers. Primary astrocytes isolated from a sEH knockout (sEH^-/-) background were also applied.

RESULTS

The immunoreactivity of sEH was increased in activated astrocytes in parallel with the progression of AD in APP/PS1 mice. Our data from primary astrocyte cultures further demonstrate that the overexpression of sEH ameliorated, while the silencing of sEH mRNA enhanced, the lipopolysaccharides (LPS)-induced expression of pro-inflammatory markers, such as inducible nitric oxide, cyclooxygenase 2 (COX-2), and pro-inflammatory cytokines. These findings suggest that sEH negatively regulates astrocyte immune responses. Enhanced immune responses found in LPS-activated sEH^-/- astrocytes also support the notion that the expression of sEH could suppress the immune responses during astrocyte activation. Similarly, sEH^-/- mice that received intraperitoneal injection of LPS showed exacerbated astrocyte activation in the brain, as observed by the elevated expression of glial fibrillary acidic protein (GFAP) and pro-inflammatory markers. Moreover, our data show that the phosphorylation of the signal transducer and activator of transcription 3 (STAT3) was upregulated in activated astrocytes from sEH mouse brains, and the pharmacological blockade of STAT3 activity alleviated the pro-inflammatory effects of sEH deletion in LPS-activated primary astrocytes.

CONCLUSIONS

Our results provide evidence, for the first time, showing that sEH negatively regulates astrocytic immune responses and GFAP expression, while the underlying mechanism at least partly involves the downregulation of STAT3 phosphorylation. The discovery of a novel function for sEH in the negative control of astrocytic immune responses involving STAT3 activation confers further insights into the regulatory machinery of astrocyte activation during the development of neurodegeneration.

Genetic and Pharmacological Targeting of Heat Shock Protein 70 in the Mouse Amygdala-Kindling Model

Inflammatory responses involving Toll-like receptor signaling represent a key factor contributing to epileptogenesis. Thus, it is of particular interest to explore the relevance of toll-like receptor ligands and modulators, such as heat shock protein 70 (HSP70). Motivated by recent findings demonstrating an upregulation of HSP70 in a model of epileptogenesis, we analyzed the consequences of genetic and pharmacological targeting of HSP70 expression in a mouse kindling paradigm. Lack of inducible HSP70 resulted in increased prekindling seizure thresholds. However, at threshold stimulation the deficiency-promoted seizure spread, as indicated by an increased seizure severity. Subsequent kindling stimulations elicited more severe seizures in knockout mice, whereas endogenous termination of seizure activity remained unaffected with duration of behavioral and electrographic seizure activity comparable to that of wild-type mice. Interestingly, HSP70 deficiency resulted in enhanced microglia activation in the CA1 region. Next, we assessed a pharmacological targeting approach aiming to promote HSP70 expression. Celastrol treatment had no impact on kindling progression but reduced postkindling seizure thresholds and enhanced microglia activation in CA1 and CA3. In conclusion, the findings from HSP70-knockout mice support a protective role of HSP70 with an effect on microglia activation and spread of seizure activity. Unexpectedly, celastrol administration resulted in detrimental consequences. These findings should be considered as a warning about the general safety of celastrol as a drug candidate. The impact of pathophysiological mechanisms on the quality of celastrol effects requires comprehensive future studies exploring influencing factors. Moreover, alternate strategies to increase HSP70 expression should be further developed and validated.

Role of epoxy-fatty acids and epoxide hydrolases in the pathology of neuro-inflammation

Neuroinflammation is a physiologic response aimed at protecting the central nervous system during injury. However, unresolved and chronic neuroinflammation can lead to long term damage and eventually neurologic disease including Parkinson's disease, Alzheimer's disease and dementia. Recently, enhancing the concentration of epoxyeicosatrienoic acids (EETs) through blocking their hydrolytic degradation by soluble epoxide hydrolase (sEH) has been applied towards reducing the long-term damage associated with central neurologic insults. Evidence suggests this protective effect is mediated, at least in part, through polarization of microglia to an anti-inflammatory phenotype that blocks the inflammatory actions of prostaglandins and promotes wound repair. This mini-review overviews the epidemiologic basis for using sEH inhibition towards neuroinflammatory disease and pharmacologic studies testing sEH inhibition in several neurologic diseases. Additionally, the combination of sEH inhibition with other eicosanoid signaling pathways is considered as an enhanced approach for developing potent neuroprotectants.

Humble beginnings with big goals: Small molecule soluble epoxide hydrolase inhibitors for treating CNS disorders

Soluble epoxide hydrolase (sEH) degrades epoxides of fatty acids including epoxyeicosatrienoic acid isomers (EETs), which are produced as metabolites of the cytochrome P450 branch of the arachidonic acid pathway. EETs exert a variety of largely beneficial effects in the context of inflammation and vascular regulation. sEH inhibition is shown to be therapeutic in several cardiovascular and renal disorders, as well as in peripheral analgesia, via the increased availability of anti-inflammatory EETs. The success of sEH inhibitors in peripheral systems suggests their potential in targeting inflammation in the central nervous system (CNS) disorders. Here, we describe the current roles of sEH in the pathology and treatment of CNS disorders such as stroke, traumatic brain injury, Parkinson's disease, epilepsy, cognitive impairment, dementia and depression. In view of the robust anti-inflammatory effects of stem cells, we also outlined the potency of stem cell treatment and sEH inhibitors as a combination therapy for these CNS disorders. This review highlights the gaps in current knowledge about the pathologic and therapeutic roles of sEH in CNS disorders, which should guide future basic science research towards translational and clinical applications of sEH inhibitors for treatment of neurological diseases.

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.

Metabolic/inflammatory/vascular comorbidity in psychiatric disorders; soluble epoxide hydrolase (sEH) as a possible new target

The common and severe psychiatric disorders, including major depressive disorder (MDD) and bipolar disorder (BD), are associated with inflammation, oxidative stress and changes in peripheral and brain lipid metabolism. Those pathways are implicated in the premature development of vascular and metabolic comorbidities, which account for considerable morbidity and mortality, including increased dementia risk. During endoplasmic reticulum stress, the soluble epoxide hydrolase (sEH) enzyme converts anti-inflammatory fatty acid epoxides generated by cytochrome p450 enzymes into their corresponding and generally less anti-inflammatory, or even pro-inflammatory, diols, slowing the resolution of inflammation. The sEH enzyme and its oxylipin products are elevated post-mortem in MDD, BD and schizophrenia. Preliminary clinical data suggest that oxylipins increase with symptoms in seasonal MDD and anorexia nervosa, requiring confirmation in larger studies and other cohorts. In rats, a soluble sEH inhibitor mitigated the development of depressive-like behaviors. We discuss sEH inhibitors under development for cardiovascular diseases, post-ischemic brain injury, neuropathic pain and diabetes, suggesting new possibilities to address the mood and cognitive symptoms of psychiatric disorders, and their most common comorbidities.

Behavioral and transcriptomic analysis of Trem2-null mice: not all knockout mice are created equal

It is clear that innate immune system status is altered in numerous neurodegenerative diseases. Human genetic studies have demonstrated that triggering receptor expressed in myeloid cells 2 (TREM2) coding variants have a strong association with Alzheimer's disease (AD) and other neurodegenerative diseases. To more thoroughly understand the impact of TREM2 in vivo, we studied the behavioral and cognitive functions of wild-type (WT) and Trem2-/- (KO) mice during basal conditions and brain function in the context of innate immune stimulation with peripherally administered lipopolysaccharide (LPS). Early markers of neuroinflammation preceded Aif1 and Trem2 upregulation that occurred at later stages (24-48 h post-LPS). We performed a transcriptomic study of these cohorts and found numerous transcripts and pathways that were altered in Trem2-/- mice both at baseline and 48 h after LPS challenge. Importantly, our transcriptome analysis revealed that our Trem2-/- mouse line (Velocigene allele) results in exaggerated Treml1 upregulation. In contrast, aberrantly high Treml1 expression was absent in the Trem2 knockout line generated by the Colonna lab and the Jackson Labs CRISPR/Cas9 Trem2 knockout line. Notably, removal of the floxed neomycin selection cassette ameliorated aberrant Treml1 expression, validating the artifactual nature of Treml1 expression in the original Trem2-/- Velocigene line. Clearly further studies are needed to decipher whether the Treml1 transcriptional artifact is functionally meaningful, but our data indicate that caution is warranted when interpreting functional studies with this particular line. Additionally, our results indicate that other Velocigene alleles or targeting strategies with strong heterologous promoters need to carefully consider downstream genes.

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.

Genetic deletion or pharmacological inhibition of soluble epoxide hydrolase reduces brain damage and attenuates neuroinflammation after intracerebral hemorrhage

Background

Inflammatory responses significantly contribute to neuronal damage and poor functional outcomes following intracerebral hemorrhage (ICH). Soluble epoxide hydrolase (sEH) is known to induce neuroinflammatory responses via degradation of anti-inflammatory epoxyeicosatrienoic acids (EET), and sEH is upregulated in response to brain injury. The present study investigated the involvement of sEH in ICH-induced neuroinflammation, brain damage, and functional deficits using a mouse ICH model and microglial cultures.

Methods

ICH was induced by injecting collagenase in both wild-type (WT) C57BL/6 mice and sEH knockout (KO) mice. WT mice were injected intracerebroventricularly with 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a selective sEH inhibitor, 30 min before ICH. Expression of sEH in the hemorrhagic hemisphere was examined by immunofluorescence and Western blot analysis. The effects of genetic deletion or pharmacological inhibition of sEH by AUDA on neuroinflammatory responses, EET degradation, blood-brain barrier (BBB) permeability, histological damage, and functional deficits were evaluated. The anti-inflammatory mechanism of sEH inactivation was investigated in thrombin- or hemin-stimulated cultured microglia.

Results

ICH induced an increase in sEH protein levels in the hemorrhagic hemisphere from 3 h to 4 days. sEH was expressed in microglia/macrophages, astrocytes, neurons, and endothelial cells in the perihematomal region. Genetic deletion of sEH significantly attenuated microglia/macrophage activation and expression of inflammatory mediators and reduced EET degradation at 1 and 4 days post-ICH. Deletion of sEH also reduced BBB permeability, matrix metalloproteinase (MMP)-9 activity, neutrophil infiltration, and neuronal damage at 1 and 4 days. Likewise, administration of AUDA attenuated proinflammatory microglia/macrophage activation and EET degradation at 1 day post-ICH. These findings were associated with a reduction in functional deficits and brain damage for up to 28 days. AUDA also ameliorated neuronal death, BBB disruption, MMP-9 activity, and neutrophil infiltration at 1 day. However, neither gene deletion nor pharmacological inhibition of sEH altered the hemorrhage volume following ICH. In primary microglial cultures, genetic deletion or pharmacological inhibition of sEH by AUDA reduced thrombin- and hemin-induced microglial activation. Furthermore, AUDA reduced thrombin- and hemin-induced P38 MAPK and NF-κB activation in BV2 microglia cultures. Ultimately, AUDA attenuated N2A neuronal death that was induced by BV2 microglial conditioned media.

Conclusions

Our results suggest that inhibition of sEH may provide a potential therapy for ICH by suppressing microglia/macrophage-mediated neuroinflammation.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1005-4) contains supplementary material, which is available to authorized users.

Deletion or inhibition of soluble epoxide hydrolase protects against brain damage and reduces microglia-mediated neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) induces a series of inflammatory processes that contribute to neuronal damage. The present study investigated the involvement of soluble epoxide hydrolase (sEH) in neuroinflammation and brain damage in mouse TBI and in microglial cultures. The effects of genetic deletion of sEH and treatment with an sEH inhibitor, 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), on brain damage and inflammatory responses were evaluated in mice subjected to controlled cortical impact. The anti-inflammatory mechanism of sEH inhibition/deletion was investigated in vitro. TBI-induced an increase in sEH protein level in the injured cortex from 1 h to 4 days and sEH was expressed in microglia. Genetic deletion of sEH significantly attenuated functional deficits and brain damage up to 28 days post-TBI. Deletion of sEH also reduced neuronal death, apoptosis, brain edema, and BBB permeability at 1 and 4 day(s). These changes were associated with markedly reduced microglial/macrophage activation, neutrophil infiltration, matrix metalloproteinase-9 activity, inflammatory mediator expression at 1 and 4 day(s), and epoxyeicosatrienoic acid (EET) degradation at 1 and 4 day(s). Administration of AUDA attenuated brain edema, apoptosis, inflammatory mediator upregulation and EET degradation at 4 days. In primary microglial cultures, AUDA attenuated both LPS- or IFN-γ-stimulated nitric oxide (NO) production and reduced LPS- or IFN-γ-induced p38 MAPK and NF-κB signaling. Deletion of sEH also reduced IFN-γ-induced NO production. Moreover, AUDA attenuated N2A neuronal death induced by BV2 microglial-conditioned media. Our results suggest that inhibition of sEH may be a potential therapy for TBI by modulating the cytotoxic functions of microglia.

Soluble epoxide hydrolase inhibition Promotes White Matter Integrity and Long-Term Functional Recovery after chronic hypoperfusion in mice

Chronic cerebral hypoperfusion induced cerebrovascular white matter lesions (WMLs) are closely associated with cognitive impairment and other neurological deficits. The mechanism of demyelination in response to hypoperfusion has not yet been fully clarified. Soluble epoxide hydrolase (sEH) is an endogenous key enzyme in the metabolic conversion and degradation of P450 eicosanoids called epoxyeicosatrienoic acids. Inhibition of sEH has been suggested to represent a prototype "combination therapy" targeting multiple mechanisms of stroke injury with a single agent. However, its role in the pathological process after WMLs has not been clarified. The present study was to investigate the role of a potent sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), on multiple elements in white matter of mice brain after chronic hypoperfusion. Adult male C57BL/6 mice were subjected to bilateral carotid artery stenosis (BCAS) to induce WMLs. Administration of TPPU significantly inhibited microglia activation and inflammatory response, increased M2 polarization of microglial cells, enhanced oligodendrogenesis and differentiation of oligodendrocytes, promoted white matter integrity and remyelination following chronic hypoperfusion. Moreover, these cellular changes were translated into a remarkable functional restoration. The results suggest that sEH inhibition could exert multi-target protective effects and alleviate cognitive impairment after chronic hypoperfusion induced WMLs in mice.

Tissue Expressions of Soluble Human Epoxide Hydrolase-2 Enzyme in Patients with Temporal Lobe Epilepsy

OBJECTIVE

We sought to simply demonstrate how levels of soluble human epoxide hydrolase-2 show changes in both temporal the cortex and hippocampal complex in patients with temporal lobe epilepsy.

METHODS

A total of 20 patients underwent anterior temporal lobe resection due to temporal lobe epilepsy. The control group comprised 15 people who died in traffic accidents or by falling from a height, and their autopsy findings were included. Adequately sized temporal cortex and hippocampal samples were removed from each patient during surgery, and the same anatomic structures were removed from the control subjects during the autopsy procedures. Each sample was stored at -80°C as rapidly as possible until the enzyme assay.

RESULTS

The temporal cortex in the epilepsy patients had a significantly higher enzyme level than did the temporal cortex of the control group (P = 0.03). Correlation analysis showed that as the enzyme level increases in the temporal cortex, it also increases in the hippocampal complex (r² = 0.06, P = 0.00001). More important, enzyme tissue levels showed positive correlations with seizure frequency in both the temporal cortex and hippocampal complex in patients (r² = 0.7, P = 0.00001 and r² = 0.4, P = 0.003, respectively). The duration of epilepsy was also positively correlated with the hippocampal enzyme level (r² = 0.06, P = 0.00001).

CONCLUSIONS

Soluble human epoxy hydrolase enzyme-2 is increased in both lateral and medial temporal tissues in temporal lobe epilepsy. Further studies should be conducted as inhibition of this enzyme has resulted in a significant decrease in or stopping of seizures and attenuated neuroinflammation in experimental epilepsy models in the current literature.

Screening of soluble epoxide hydrolase inhibitory ingredients from traditional Chinese medicines for anti-inflammatory use

ETHNOPHARMACOLOGICAL RELEVANCE

Inhibition of soluble epoxide hydrolase (sEH) has been extensively reported to be anti-inflammatory in multiple animal models. Some anti-inflammatory traditional Chinese medicines (TCMs) and a few natural compounds were also found to be inhibitory to sEH in vitro.

AIM OF THE STUDY

To determine whether the active intergradient (AI) against sEH of anti-inflammatory TCMs in vitro is anti-inflammatory in vivo and the sEH inhibitory action of the AI contributes to its anti-inflammatory effect in vivo.

MATERIALS AND METHODS

In vitro inhibition assay of the sEH was conducted for the methanol and ethanol extracts of 27 anti-inflammatory TCMs. Two potent extracts were subject to further separation guided by bioassay to afford promising AI against sEH in vitro [Fr.5 of the crude ethanol extract of Rhizoma coptidis (FFCERC)]. Finally, the in vivo anti-inflammatory effect and sEH inhibitory potency of FFCERC was evaluated in a lipopolysacchride (LPS)-challenged murine model of acute systemic inflammation. The inflammatory status was characterized by the inflammatory cytokines TNF-α and interleukin-6 (IL-6) and sEH inhibitory function was evaluated by the plasma levels of epoxyeicosantrienoic acids (EETs) and dihydroxyeicosatrienoic acids (DHETs), which are the sEH mediated substrates and products, respectively.

RESULTS

At the concentration of 25µg/mL, the crude ethanol extracts of 6 TCMs including Herba Asari, Radix Polygalae, Fructus Amomi, Radix Astragali, Radix Scutellariae, and Rhizoma Coptidis were potent against sEH. The crude extracts of Herba Asari and Rhizoma Coptidis were selected for further separation to afford FFCERC as the most promising AI for in vivo evaluation. Oral administration of FFCERC attenuated the significant increase in TNF-α and IL-6 caused by LPS challenge in a dose-dependent manner. In parallel, oral administration of FFCERC shifted the changes in plasma levels of EETs and DHETs caused by LPS-challenge like a synthetic sEH inhibitor.

CONCLUSIONS

A sEH inhibitory AI from Rhizoma Coptidis is anti-inflammatory and the inhibition of sEH contributes to this biological effect, indicating that sEH may be at least one of multiple therapeutic targets for relevant TCMs.

Intraperitoneal injection of IL-4/IFN-γ modulates the proportions of microglial phenotypes and improves epilepsy outcomes in a pilocarpine model of acquired epilepsy

Recent studies have reported microglia that are activated in the central nervous system (CNS) in patients with temporal lobe epilepsy and animal models of epilepsy. However, limited data are available on the dynamic changes of the proportions of various phenotypes of microglia throughout epileptogenesis and whether IL-4/IFN-γ administration can modulate the proportions of microglial phenotypes to affect the outcome of epilepsy. The current study examined this issue using a mouse model of pilocarpine-induced epilepsy. Flow cytometry showed that classically activated microglia (M1) and alternatively activated microglia (M2) underwent variations throughout the stages of epileptogenesis. The altered trends in the microglia-associated cytokines IL-1β, IL-4, and IL-10 paralleled the changes in phenotype proportions. We found that intraperitoneal injections of IL-4 and IFN-γ, which have been reported to modulate the phenotypes of microglia in vitro, also affected the proportion of microglia in vivo. In addition, correctly timing the modulation of the proportion of microglia improved the outcomes of epilepsy based on the reduced frequency, duration, and severity of spontaneous recurrent seizures (SRS) and increased the performances of the mice in the Morris water maze. This study is the first to report altering the proportion of microglial phenotypes in pilocarpine-induced epileptogenesis. Intraperitoneal injection of IL-4/IFN-γ could be used to modulate the proportions of the types of microglia, and epilepsy outcomes could be improved by correctly timing this modulation of phenotypes.

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.

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.

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.